choice for thee, but not for me

We've all heard some side to the "people choose to be gay" argument.  I agree with those that have said that it's not even a worthwhile argument.  Does it matter if it's a choice?  If I choose to play dungeons and dragons as a hobby, does that mean it's perfectly legitimate to outlaw it for no good reason?

We all know what "you choose to be gay" really means.  It's the last gasp of a dying conscience.  It's a person who realizes that he is doing some very uncool things to a fellow human being.  It is someone who is free to engage in socially and governmentally sanctioned relationships who is working to deny the same ability to a whole class of people.  And at some point he realizes what he's doing.  He's working to harm other people.  And he has a choice.  Stop trying to do evil, or rationalize it.  Sadly he chooses to make himself feel better instead of making the world a better place, and he does it by telling himself that it's really their fault that he's doing this to them.  If they'd just stop being gay he wouldn't have to work to dehumanize them.

But still something has always bothered me about this.  I mean, the argument carries with it the clear assumption that the person using it understands sexuality to be a matter of choosing which gender to get into sexual relations with.  It implies that the person making that claim is equally attracted to both genders.  That he chooses to be straight.

I tried asking someone on youtube this once.  He'd pulled out the choose to be gay argument, and I asked him if he realized that that implied that he was gay.  He just said something to the effect of "you must have misunderstood me" and restated his argument without changing anything.  It was still there, the unstated assumption that all people choose which gender to be sexual with.  We went around and around like this, with him refusing to even indicate that he understood what I was saying, until I got exasperated and asked him point blank if he chose to be straight.  Nope, he told me.  But he couldn't let it go at that, he had to follow it up with an assertion that gay people do choose to be gay.

I don't really know what to make of this.  I feel like he was genuinely puzzled.  He seemed to be a legitimately straight individual, but somehow he didn't see the hypocrisy in demanding that while he can't choose which gender to be attracted to, gay people absolutely can and do.

Is it a failure of empathy?  Forgetting that GLBT people are even human?  Have these people gotten so accustomed to thinking of GLBT people as "the other" that they casually assume that they must be governed by a completely different set of primitive drives?  No, that doesn't work, because if they believed that then they might be willing to consider that some men want to sleep with other men AND NOT WOMEN.  But that thought never seems to come up.

So what is it?  A lack of curiosity?  An unwillingness to question their own biases?  Knowledge, on some low level, that this is a bullshit defense that doesn't even make sense, but also knowledge that this is what allows them to not see themselves as monsters, so they refuse to let it go?