I've always been happy eating peanuts, but that doesn't mean I'm going to go shove them down someone's throat and give them anaphylactic shock (whoot, spelled it right on my own!). (Ok, I can think of precisely two people I would do that to. But that's not the point.)
Just because something works for, say, 90% of the population and not for 10%, does that make it ok? I'm not saying we need to get ridiculous and have dolphin bathrooms. There's only so much we can accommodate, as a society. But I think we can at least let people make individual choices, so long as they don't inconvenience everyone. As a gay person, I would be pretty fucking pissed of if some straight person came up to me (as in times passed) and said, "Look, this works for 90% of us, so it had better work for you, too." (Come to think of it, that does happen to me. But I can still go home and fuck my wife.)
Back to the peanuts: just because they work for 90% of the population, they still make 8% of the population uncomfortable and kill 2%. It's the same with gender. (No, I don't know the actual statistics of peanut allergies.) Sure, 90% of people (or whatever) are perfectly happy with their bodies (or at least their gender. Maybe this whole fat thing really -is- women trying to make themselves more like teenage boys?). Great for them! Seriously, I'm happy and I wish them the best. Being happy isn't a bad thing, and being content with who you are is great.
But then you've got another 8% who are uncomfortable with their 'gender identity'. And 2% who, if they can't change, don't find life worth living. So they should just buckle under, because they've got the other 90% telling them how happy they are?
Shouldn't we be surprised (I don't remember where I read this first, so I can't give credit, sorry) that more people aren't unhappy with a binary definition of gender? You're either pink or blue? Sorry, no purple or green or orange.
What if one day we woke up and everyone had a mark (like a My Little Pony), and this mark indicated the job you would have for the rest of your life, and there were only two: janitor and carpenter. The carpenters build everything, and the janitors clean up.
People would freak!
"Yesterday, I was a nurse and now I'm a janitor? Screw that!"
And no, you can't change and go from being a janitor to a carpenter, or vice versa. Sorry, it's done. That's what you are. One or the other.
The only reason this works for gender is that we didn't just wake up and find it this way. Everyone has already been marked janitor or carpenter from the beginning, so they just go with it.
But some people can't. Some people want to be the other job, or be a welder, or a ballerina. And what's wrong with that?