Anyone can choose to have sex with anyone they choose. They still have an attraction towards one sex or another.
I agree with you here.
The difference is that I recognize that people are defined by what they do and not by attraction, feelings, or what they say they are.
So if you have gay sex, are you always gay then? Since we're comparing the two. A criminal is someone who has committed a crime.
Not unless you continue to have gay sex or be in relationships with someone of the same gender. A criminal doesn't always remain a criminal, either. People's decisions can and often do change over time.
Being a choice is not an argument for or against anything.
Maybe not for you, but there are MANY people who believe that because sexuality is a choice it is perfectly legal and correct not to allow same sex marriage.
Again, and I really mean no offense by this, but try thinking outside your own limited perspective for once.