If that was the case how do you explain homosexual people. Are you saying that arnt born one way or another because I know there is a whole bunch of people that would disagree with you.
I think people are born what they are whether they be straight, bi, gay, trans or what ever else there is. The guys that lead a public life of being straight but do things with men on a regular basis are still bi and they most likely know it but just choose to not share it.
Some might even just say that they are straight because they know gay men like even thought they know it's not true.