Aight, I got a very simple reply to this. People dislike Veibae not because she's sex positive, but because she's positively annoying.
Let's go further and I'll say, I've seen very few really damning sentiments on Melody in this thread. Guess what, unlike Veibae who uses sex as a joke, Melody just is sex obsessed, but has a really nice and nuanced personality. She is a nice person who also loves sex, which is grand. There ya go, that's why Veibae bad and yet Melody not bad.
Edit: Anyone trying to push puritanical views because of Hololive would be stupid, we have three Holos (Mel, Choco and Noel) who through ASMR effectively sell sex. Once again, they also have amazing personalities and try to entertain people.