I recently ran across a comment on another MMO blog where they were discussing the item shop in GW2. I thought my response did a good job of summing up my arguments against cash shops in general, so I reposted it here.
"Explain to me how someone else using an EXP boost or anything else from the cash shop is negatively affecting your game play experience. Keep in mind that in PVP you get auto brought up to max level, and that you're never competing with anyone on your server."
To do so would first require you to accept the premise that there are other possible forms of achievement in these games besides conquest in combat. In some older titles, you could play to be the best dressed, play to dominate the market or play to be the crafter that outfitted your guild all in black.
This current view that all things cosmetic do not affect game play belies the major assumption that the only thing of value achievement-wise or competition-wise is combat because these item shops completely bork all other play styles.
Even tossing all that aside, if you can accept that people play for different reasons than yourself and value their fun as well as your own then you can see that many, many people play to hit cap first or for play for guild or server 'firsts.' In the case of XP boosts being available for cash, this play style is completely screwed as players or guilds with more disposable cash have a better chance to get there first by directly buying it.
Even if you don't consider these valid goals (it's not why I play either) saying that XP boosts don't affect game play means that they don't affect YOUR game play therefore the converse must also be true - removing them wouldn't affect you in the least.
But they have to make money!!! you say.
I agree and they should be paid well for good work. Make it a sub game and kill the cash shop.
In a nutshell, this post highlights the major reasons I'm against cash shops in any form - they limit the valid play styles. Anything available for cash removes an achievement type from the game and hands it over to people with more cash than common sense who want to treat MMOs not like virtual worlds, but like Dress up Barbie joins the Army.
This has the direct effect of homogenizing the player base down to people who only value combat as an achievement or in competition. It kills the variety of the player base and is precisely why these games are feeling so anemic.
Buying something for cash in a game is the real world equivalent of having everything handed to you. There's just nothing left to do in these games that's worth doing except to fight.