There are a few reasons why players seem to really dis-like RMT, but from most of my experience, it comes down to these main three:
1) Players that spend money in cash-shops (I use cash shop to indicate any form of RMT, meaning actual cash-shops or character purchasing services just like in EVE) gain some sort of "advantage" over players that do not spend the extra money.
2) Cash shops encourage addictive spending.
3) Non-spending players, and their accomplishments, are devalued.
First of all, in order for most of these arguments to work, you must establish a certain set of rules or goals that MMORPG's set, in order for there to be something to "succeed" at legitimately so that someone can "cheat" by buying their way to that goal.
But there are no Golden Rules or Golden Goals in any of these MMO's. The closest any MMO comes to are in games that are only actual competition, like in kart racing mmo's or pvp-only games, but those games are very very rare. Even then, there are ways to play that do not fall within the boundaries of the goal, and many players playing in many different ways.
For an example, a game like WAR might be talked about as though PVP is the way to "win" at the game. But, that is not the only thing to do in the game, and even within pvp there are goals that can be set by the player (i.e. playing naked, racking up deaths instead of kills.) In WAR you can do PVE content and have a grand time, and in most MMO's you will hardly ever HAVE TO do anything. The only way an MMO can force a goal on you is to stop you from playing their game if you do not play within a certain set of rules. The name of the game(s) is to exist within the world, not to do certain activities.
That's why checkers sucks as an MMO: there are no choices, and only one true goal.
In a game like Vanguard or WoW, for example, many players say that the "goal" is to "beat" the end-game. Of course, that is only true for those players that decide to attempt that goal, and not for players that simply do other things.
(In a funny side example, my ex co-host Luper had asked lead developer Silius for some visual variety in a certain classes highest level uber armor, and he simply answered by telling her that if you go after a certain set of armor, you might look the same as the other players going after that same armor. In that case, yes, there is a set of rules, guidelines and standards, but only followed by those wanting to play in those very strict boundaries.)
Things like official leader boards or progression threads are used as evidence to prove that the game developers themselves give in to the idea that "end game" is the true goal of the game, but those are just tools, and again are only useful to those players that want to live in that section of the game.
All this is to say that even the most basic MMO has not only a million things to do and variables OF those things according to each player, but a rare few MMO's have one official goal or activity that everyone MUST do. Can a player gain advantage over another player within certain spheres of play using cash shop items? Of course. But let's talk about some examples of things that players have been doing, since the beginning, to gain an "advantage". This is a small list, but I will promise you that most players, even the toughest RMT critics, have done one or several things on this list. Most of the "advantage" criticisms come from a financial stand point, meaning that most critics feel like one player can gain an advantage simply using real life money.
1) Buying/using a second account: Since the beginning players have been using two or more "extra" accounts for dual (or more) boxing, or for the extra inventory space. I know, personally, several players that cannot stand any form of RMT yet have been using dual accounts for years. Guess what? Spending an extra 15 dollars a month on an extra account (for space or for dual boxing) is the exact same thing as spending 15 dollars a month on "extra inventory space" items from a cash shop or as buying characters. Whether the player has to level the character or not does not matter.
2) Purchasing a better connection (ISP's will provide a higher bandwidth connection for more money) or better PC equipment: How is this NOT an advantage? For all those that would laugh at this idea, none of them can deny that a better connection and a better PC can physically, more than anything, effect performance. If you are lagged out, it doesn't matter what level you are. Yet, according to some critics of cash shoppin', spending an extra thousand on a better PC is nowhere near the sin of buying an extra health potion. In fact they would be right and ironically this example proves my point in favoring cash shops by saying that the developers cannot control how far players will go to actually gain an advantage, and many have been purchasing advantages for years.
3) Purchasing a "limited edition" or "collectors edition" game: This is the most blatant form of RMT that most critics participate in. Yet, this is never seen as cash-shoppery, although in this case it is literally an example of a player being able to go to a REAL shop to spend REAL cash. Look at any collectors edition and you will see how they entice players to spend extra dollars for special, in-game items. While me and Leala stood outside of a Game-Stop, waiting for our copy of The Burning Crusade, a super nerd came out of the store with extra copies to sell to players right there in line. One player gave him a few hundred dollars JUST for that limited edition. Some items have actual stats and look cool, (see the special cloak that came with the Mines of Moria limited edition) making that real money transaction all the more delicious.
These are just basic examples, but anyone can see that the principle is the same. As soon as you hand over cash to a company in return for virtual goods, even if those virtual goods are a pass to play for a certain amount of time, you are participating in RMT.
Even your avatar in most MMO's is a form of cash-shoppery.
When you start out in almost any MMO, you have already paid 50 dollars for a box. What do you get for those 50 dollars? Certainly not just "access" as many critics would put it. You get a character, maybe a few special items, and of course all the newbie gear (in most MMO's, not all though) that you can handle.
Most would laugh at newbie gear being considered for anything more than well, newbie gear, but the actual value of that gear is not set to "low." I know many players that held on to their beginning gear out of sentimentality, (the equivalent of a fluff pet) and a player could actually use that newbie gear for their entire career. There is no rule that says your gear has to be of a certain stat level, again proving that most MMO's have no rules.
I wish the critics would just come down to say it, but many of them don't: "I don't want another player being either able to kill me faster because of something they bought in the cash shop, or a player to be able to buy something I "worked" hard on to get." That's fine, just spit it out.
But if we are talking about advantages here, and mainly financial ones, my point is that players have been using money to gain actual advantages since it was OK for a player to stay up for 4 days camping something.
There is no more noble way to spend your cash, or a way that is more or less "cheaty." That doesn't apply because not only are there no official goals (meaning forced by the game) in most MMO's (look at how much success that brought to Fury) but even within games that have many popular activities, there are ways to play outside of those activities.
Let's not let this argument be about "one player is spending money to gain an advantage.." as though cash shops are the great enabler, allowing the sneaks and the lazy to suddenly bask in the glory that the "hard working" bask in. If anything , cash shops level the playing field so that anyone can play how they want. Everyone has equal choices. (And no, using " Let all the Olympic athletes dope up, then..." argument does not apply. After all, that's real life and dangerous, but in the Olympics you have one finite goal: the gold medal, and one chance to get it. In MMO's you have as many chances as you do lives, and you have countless lives, as well as Gold Medals that never end. There are gold medals available to all who want them.)
One cash shop critic commented (basically) that he thought that most cash-shop games are bad because eventually you are forced to buy something out of the cash shop in order to "succeed." (Of course, there is no over all success, being that a player can set his/her own goals even within official ones...something we cannot do in real life in actual competitions.)
My point in response was to allow him that...the idea that players HAD to buy something eventually. So, why wouldn't he just call it a "subscription with timing freedom"? In other words, a sub that HAD to be paid (just like a regular sub) but only upon reaching the point the "success" was the goal.
Let's face it, there is just something about cash shops that some people will always feel are bad.
But critics have to stop and think of all the things that are actual part of a real money transaction. They need to ask "Is a subscription a form of RMT?" or "Have I ever paid for an in-game item, in a collectors edition? Or, if not, why don't I have an issue with it?" or of course: "Do I have an issue with second accounts/faster PC's/or dual boxing?"
Players have been participating in cash shops (blanket word, people!) since the very beginning. In no game do you only pay for "access." If that was the case, you would log in as a spirit, freely floating about the world, looking for a body. You pay for that avatar, that newbie armor, that free house, that limited edition pet, those special veteran potions you get at a year, and many, many other items.
On a side note: why do so many critics of cash shops seem to forgive EVE and it's blatant example of cash shoppery? As a matter of fact, those defending EVE often have issues with OTHER games that sell entire characters, (Vanguard for example) but forgive EVE. Why?
My gut tells em that EVE has simple nerd cred. That game is often touted as deeper than it is, funner than it is, and more honest. It is said to have "meaningful PVP" (meaning someone can hold your ship still, kill you and take your stuff) and also said to have true "sand box game-play" (set, of course, within the boundaries of space, a ship, and the physical rules of the game.) All of these are true in some way, and false in many other ways. But they did something right to be able to pull off one of the biggest cash-shop infusions and to escape with less criticism than most.
Here, I'll say it: EVE is a cash shop game just like Ether Sage Online, Mabinogi, or Dream of Mirror Online. Actually no, EVE sells entire characters, those examples don't.