Well from my point of view, if you're straight, you are straight. And if you're gay, you're really gay. No matter how many porn videos you watch, what you are or what you really like will prevail.
What about those people who lived half their lives as a person of one sex and then decided that they really want something else? Do you believe that deep down they were always a woman, not a man, just pretended for 30 years? I think that in some cases people are influenced by the society to undergo the procedure and change sex. They may be uncertain of it and thinking about it but then something or someone pushes them to do it.