It needs to be taught if you want to learn how to use it, but everyone has the potential to use at least one kind.
You haven't shown that 'mental fortitude and sheer strength of will', in and of themselves, are a defense.If you want to get generic, it's an outside force that's trying to knock Superman out. He's met such things in the past and conquered them through his sheer willpower. Haki isn't an instant win button even in One Piece. And there's no indication that it would have any effect on somebody with as much mental fortitude and sheer strength of will as Superman.
Your debates are all flawed because they are based on rules with flawed assumptions. If you assume something silly, like 2 + 2 = 5, you can actually build a consistent system of mathematics around it if you try hard enough, but it has no relation to real math.We have real debates here everyday that follow the rules. And people only get banned if they're being assholes. If you don't like the rules and don't want to follow them than that's your problem.
Besides, you guys have been threatening me with banning just because I don't believe in silly things like non-combat feats automatically prove combat speed, and characters who get tagged by normal humans all the time aren't actually fast in combat. If that's what is meant by being an asshole, then you have a weird definition of it.