"Even if a person is homosexual, they are demonstrating that by conducting an activity in private."

So, is a person only homosexual when they are having sex with another person or looking at porn or something?

You saying they are not the same as someone born with black skin is an opinion, which you are unable to back up with anything other than just what you believe.  Homosexual activity is found all throughout nature in different ways, all over the world - is it really that hard for you to believe that as humans, with a much more evolved brain than any other animal on this planet, we are sometimes born being attracted more to people of the same sex?