I imagine you'll take this as me using truth to justify being mean, because that's a thing that people do. That's a thing that I have done, when I was much younger.
But I insist that it isn't the case. I have no particular dislike of Reimu, and I enjoy interacting with her sometimes. I don't derive any satisfaction from cruelty for cruelty's sake. Even if it can be immediately satisfying, lashing out for the sake of lashing out has always left me feeling hollow afterwards, as you yourself describe. I enjoy discussing the unusual character of the posters here. I think they're interesting, and there isn't any malice in it. But I don't feel guilty about not mincing words, or pressing them a bit if it means they will show me how beautiful they are.