I would argue that this is their problem, not yours.
Again, that is their problem. Also, there is no reason to believe that said players would bother with the content even if they couldn't buy the boost.
While I understand this concern, I don't think this is the fault of people buying boosts. If someone chooses to buy boosts to get raid gear, mounts, achievements etc, then it likely means they can't or won't raid properly. Either way they were likely never contenders for recruitment. And even if they were, do you really to recruit someone who is only grudgingly doing raiding to get some gear? If they would rather pay gold than do the actual content, they're not likely to show the kind of committment most guilds are looking for anyway...
Which is fine. One of the points of an MMO is to provide a number of ways for players to get fun out of the game. Not everyone has to enjoy and participate in every aspect of the game, simply the parts that they do enjoy.
Personally I think that if people are not interested in doing challenging content then they shouldn't be doing it. I get that for some people, part of the fun of beating the challenge is getting to show off (with a mount, title, fancy gear etc), but still, they do have a desire to do the actual content. I certainly don't want to raid with people who have no desire to actually raid and engage challenging content. If all they're after is some gear, or a mount, or achievement, then I am 100% fine with them buying a boost to get those things. We can fill our raid spot with someone who wants to be there.