Honestly I don't see why they're a problem. I've never touched one and relish the feeling I get when I finally beat a particularly hard encounter, but not everyone is the same. If someone wants to throw around gil in order to beat an encounter they're having trouble with or want the mount from, that's their right. It's not like house selling where the RMT element is deliberately withholding a piece of content from the general public in order to turn a profit. The people who sell runs generally will never mix in with clear groups. Plus, like Jeykama said it's a legitimate way for people to earn in game cash.