Myth 1 - Homosexuality is a Choice:
If that's true, then so is heterosexuality.
People who are gay cannot help being gay. Whether it is caused from birth or is developed is irrelevant. The fact remains that it is beyond the gay person's control. It is not something they can choose.
If a person is not free to make a choice then they logically cannot be held responsible for the consequences of the 'choice' they are forced into. Therefore it cannot be 'wrong' of them to be gay.
Ridiculous things like conversion therapy can be psychologically harmful and so called "successful" converts simply repress their self, and later go on to commit suicide because of it.
Myth 2 - Homosexuality is Harmful:
So far, the death and injury toll for being being harmed by other's homosexuality or their own is... none.