Wow. Let me just start by saying something I know you must realize: that is royally screwed up. Do you not dress masculinely in everyday life? Is cosplay not dressing up like a character who is NOT you? They're just abusing their parental power now... I side with Josh, if you can get away with it, just lie...
"- The idea that my frontal lobe hasn't fully developed yet, and therefore I'm not mentally equipped to know for sure that I'm male"
How old are you? Late teens? Are you prone to impulsive decisions or bad judgement? These are the signs of a not-yet-developed frontal lobe. Something as fundamental to identity as your gender would have developed long ago. In fact, personality is formed (and relatively difficult to change) around age 5. Tell them to research it themselves, or you could provide them with a source.
"- The idea that binding is physically unhealthy for me and is going to do damage"
They are aware that you're going to, after becoming independent of them, have surgery regardless of their wishes, yes? You would have to bind excessively over a period of years to cause damage, and even then, you aren't damaging anything you plan to keep. Perhaps, if you think it would get through to them you could try relaying to them the psychological effects on you when you're not bound.
"- The idea that I've been convinced of my identity by online groups"
Again, personality is formed at a young age. Have you been butch and/or had some sort of characteristic behavior of other ftms when you were little? Remind them of things you've done that overtly indicate your "trans-ness" that existed either before the internet or before you came out.
"- How to get through to them just how psychologically damaging it is to have to suppress such a basic part of my identity around them"
That's a tough one.... just speak from the heart I guess. Tell them, in your own words, how you really feel. That's really all you can do.
- The basic theme that I have to "wait to be a boy" until I'm financially independent
Yeah, that one sounds familiar. You're a boy now. No amount of calling you she or forcing you to dress up as a feminine anime character will change that. All they are doing is delaying the inevitable and pushing you away.
Hope this helps... I've been badgered with similar questions. Thank God, as much as I doubted their ability to do it, my parents have actually come a long way. Not to acceptance just yet, but at least to tolerance.
Good luck. Try not to let them get to you.
