It suppose it is easy for the bronies to think that Rarity is not generous because she is a bit of a snob, but being a snob and having high standards does not make someone not generous. The two are COMPLETELY unconnected. I have a very dear friend who is extremely giving of herself, but can be a down right snob. She doesn't like wearing hand-me-down clothes, buys super fancy and expensive purses and wallets, and so many other things that would cause people to believe that she was completely selfish. It's not the case. She is truly giving and tries to make other people happy whenever she can.
There is also a side to Rarity that I'm not sure everypony sees. She's a perfectionist, to be sure, but she is also a tiny bit insecure. More than anything she wants to be an important pony and she thinks the only way to get that is to be so critical and exacting in her standards. If everypony remembers, she doesn't exactly come from the classiest of places or the classiest of parents. It's like she has to go out of her way to make herself look important and do anything within her power to BE important. Sometimes that can make her come off as non-generous, but that doesn't having anything to do with it either. Someone's aspirations and how they earn them doesn't take away from their generous nature.
Somepony can have very high quality taste, be picky, whiney and many other things, but that doesn't stop them from being generous. I think if everypony just re-watched the episodes with a different eye, they would see Rarity is very generous AND a snob.
