I think the "friend zone" exists, and both genders are at fault at its creation, assuming we are talking about the stereotypical heterosexual female puts male in friend zone deal.
Sometimes you could just genuinely be friends with a girl then have it develop into something more. It's understandable considering how close friendship can be, they are not that different in my eyes except one is exclusive and involves sex as well as the whole share feelings crap. If so it's unfortunate if one person just want to remain friends, but I don't think you can somehow charm them over like you're gods gift to women. They've made up their mind.
You can try be friends if you want but the rejection is explicit and for me even more offensive than someone saying no in an outright fashion. Oh, you like me but not as much as I like you? It's pretty demeaning, I would rather get a simple no, once that person has a romantic status in my mind it's all or nothing, I won't stand for getting screwed around and friendzoned. No we can't be friends, sitting around being a bitter little maggot pretending to be "just a friend" while desperately hoping to jump in as soon as the fickle beast of the rejector changes her mind is just low conduct.
Guys(rejectee): If it's possible be forthright with your intentions , you either express interest sexually from the start or don't act like a sissy and whine when you approach her as a friend then escalate and get offended when she only sees you as one. Act like an adult and move on. Sometimes the friends--->relationship approach might work or be inevitable if she was really only your friend to begin with but don't be childish if it doesn't.
Girls(rejector): Don't friend zone people! If somebody expresses romantic interest than they care about you a great deal more than you do for them. It is not a solution to say "Can't we just stay friends?" Don't keep their hopes up by trying to remain some semblance of affection as friends, you either take their offer or you don't. If you don't think of someone sexually then break it off completely. It's the kinder thing to do.
The friend zone is a creation of people who do not know how to handle rejection or rejecting people. If we were all mature about the fact that we aren't meant for everyone then this wouldn't happen.
I mostly agree with what O07_eleven is saying here. I just want to add that it's OK to want to retain a good person as a friend. It's a natural thing,
maybe you don't share feelings, but you do share something in common. It's just
not OK to expect them to be happy about it, expect things to "stay the same", or expect to keep them on the back burner in case your current love interest turns out to be a
bad match.
I for one don't believe it's right or healthy to relegate anyone who expresses interest in that way to the friend-zone unless they choose to be your friend. I'm sorry, I know it's awkward and it tugs at any reasonably empathetic person's heartstrings, but a clear no is more often the safest way.
If you don't feel safe with that, you should get help regardless of whether that help is a cop or a shared and wiser friend or two.
In the end it's possible to say "No" and still be friends. It's just not a good idea to say "No" and say they're just a friend.
If you're the rejector, do them a favor and
give them a solid reason why you do not feel that you are a good match for them. Be kind and honest about it, and they'll most likely respect you for that. If you examine your reasoning and feel bad about giving it to them, feel free to re-examine your reasons if you feel them to be unfair, in the end you should still feel empowered to say "No" for any reason. Maybe your real reason is not the one you thought it was, but don't hurt others by saving face and lying to them about why.
If you're the one being rejected, please do them a favor and
don't take it personally. It's not always your fault that they might feel you're a poor match for them; it could be a diverse number of things including circumstances affecting impressions, things other people say and do, their own state of mind, and even their own feelings for another that may perhaps exist or still linger. There are many things beyond one's control that often determine your luck at finding a partner, and there's always another match somewhere if you look hard enough.