Sorry in advance Scndthe2nd, because I’m going to break down your posts to best answer your question.
Why is the vagina the isolating factor in this discussion? Why is whether a person has a penis or not a qualifier for the group—and how do you enforce this?
If you ask that question then you have to ask, “why is a penis the only reason a man can’t join women’s sports?” It’s not just the penis, but the entire physiology of a man differs from a womans.
Whats your views on people like Jazz, who commit fully to their chosen gender? http://jezebel.com/5862815/meet-jazz-an-impressive-11+year-old-transgender-girl
It makes no difference to me how a person wants to live their lives, so long as it doesn’t hurt another person. I don’t think it would be fair of Jazz (when 18+ years old) to lure men into a sexual relationship, only to reveal later that he is really a boy.
Whats your thoughts on people who have 5a-dht deficiency as a fetus, so have the gear and tackle of a man with the neural structure of women?
This is where the ambiguity of gender becomes even more skewed. I appreciate just how complicated this all can get. This is one where I say let the true sex of the person reign and though. Earlier someone tried to bring up the argument of the hermaphrodite, butI won’t argue the point, because it isn’t relevant to the transgender argument.
Also, i’m not sure, but I think in general, when talking about transgendered people, you refer to the chosen gender rather than the sex. Its like that in transhuman rpg, i would think that would relate to real life too. I could be wrong, and i might actually agree with you—that a transgendered boy should not be in girl scouts, because that child hasn’t chosen to be acknowledged as a girl, but as a boy instead.
Thinking in that way gets you a witch hunt against you on this board. 
Still, i think limitation on such children’s activities is wrong regardless of the social stipulations you try to stick to it. The goals of these groups should be attempting to teach skill, creativity, survival and fairness, and discrimination doesn’t lend itself to any of these goals. But that’s my opinion.
I agree with teaching people acceptance, but I disagree with this group when it comes to special treatment for certain people due to their lifestyle choices.