I don't see the character I play as me, I see it as a hero in a story. Sometimes the hero is male, sometimes female, sometimes they are an anthropomorphic cow, troll, space goat or whatever. I may like the way one model looks over another, or their animations, but I don't identify with their sexuality.
I think another reason I pick females, is that I have a thing for stronger girls. Girls who can take care of themselves, girls who you don't have to worry about, girls who can kick ****. I just have a thing for that, and many of these video games are awesome in the way they let you choose which you want to play.
None more kickass than Female Commander Shepard though. I've never had so much awesome fun with a game storyline until I played Mass Effect with a female character. lol