Actually, yeah, it's a pretty common reaction with girls in anime and manga, even those clearly straight.
I think the point isn't about not to appear slutty, but because those guys are only interested in sex, and they would rather have romance.
Correct me if I am wrong, really, please do, I want to be informed on this stuff because these assumptions are entirely grounded in the things that I have a "gut feeling" on when reading and my very basic knowledge about japan and it's culture but I feel like this is one of the many "pitfalls" you can fall in, given how anime and manga really more often than not try to push and encourage Wife-material, the loyal yamato nadeshiko big boobs, perfect body and pornstar hair not entirely optional or as I said, desirable female
Well, I can only give my opnion there, since everything else will be speculation, unless I actually make an interview with japanese people. (I don't think I ever read one about that).
But yeah, I think you're kinda right about that, but not entirely. Yeah, this kind of character is more desirable, sexually or romantically, but I think that in general, they're more sympathetic to their target audience. I say that because even male character on shows targeted to men are like that, not having a lot interest in making sex with a lot of girls and being more interested in romantic. Except in some more niche titles, the pervert character will usually be a stupid guy that will only end up bad.
I don't think this is a japanese thing, though, but a nerd thing. Just look at 4chan and how they hate those "normalfags" with their active sex life.
Even yuri titles clearly aimed at female usually fall on this trope, so it's not a thing to male japanese otaku either.
Actually, the people here on dynasty aren't different at all. Most work that feature more sexually opened characters will have a lot people hating on it.
But anyway, in this case in particular, these guys hiting on random girls at places are usually creepy and just want to use them, so I think it's natural to avoid them.