Well, I'm not a cosplayer, but there is one character I always wanted to "cosplay". And so if I finally step up and do it, it will be very likely, that I buy most of the stuff and not try to learn how to sew my own costumes. (hopefully it is not addicting ... :P)
So I don't know who "hates" on cosplayers that work with tailors or similar.
It's probably a question how much "model" and how much "creator" is in a cosplay!? I'm not that "deep" into the subject. Where is the border between some people, that sew their own costumes in month of work and go to one con in a year. "Professional" cosplayers, like you, where you are paid to go to a con and show your newest design (that is probably created by a different person). And "booth babe"-models, that just wear what people gave them.
Where is cosplay ending?

As someone who has both worn premade and homemade costumes... I kinda disagree, on a personal level.

Don't get me wrong, I don't mean that I go around turning my elitist nose down on anyone walking out of the dealer room wiearing an eveelution hoodie, that's not what I mean, But it's definitely much less self-gratifying, you know? Getting a compliment on something I've sewn together makes me more confident in my skills, getting props for something I've ordered just makes me glad I have a paycheck.

Besides that, some of the best parts of cosplay is messing up. I've done some cosplay so hilariously bad it's left me in stitches.