OK, when a person is longing for and looking for a sexual/romantic partner, it's not uncommon to have some desired partner show no sexual interest and, sometimes, to say 'But I think of you as a friend.' And it's true that this is upsetting and frustrating. But, you know, tough shit! No one is obliged to fancy you just because you fancy him/her. It's perfectly possible for an acquaintance to like your company, appreciate your intelligence/sense of humour/shared interests but still not find you sexually attractive.
FFS it's happened to me enough times - a man I thought was utterly gorgeous, funny, charming, smart, and who was happy to chat to me and hang out with me would not want to have sex with me. I didn't like it when it happened, but I would just have to suck it up and get over it. And not blame him. Plenty of men experience similar frustration and hurt feelings when a woman refuses their sexual advances without being arseholes about it.
As to the point about 'friendzoned' men often being complete fucking mingers, there is a little bit of a cultural trope going on for women, though, that the answer to being 'friendzoned' by men is to Get Thin and Go Shopping (which doesn't work, any more than whining and begging does, if someone doesn't fancy you). Women are still expected to change their behaviour and appearance to please and attract men, whereas men are not - and so many of the type of men who sulk and tantrum about women friendzoning them aren't even prepared to have a bloody bath before going out to socialise. They don't seem to understand the basic concept of women's sexual autonomy - that women choose the partners they want for a variety of reasons. Bitter whiny men also focus intensely on women who are quite simply Out Of Their League - much younger than them, beautiful, popular, successful - without being able to understand that having nothing to offer other than 'niceness' is simply not enough, and then hate these women for wanting partners that they actually fancy.