Humans are the most unnatural organisms on the planet, we don't live in harmony with nature at all. We have modern medicine that allows people who should have died to continue living, we have antibiotics to fight infections that would have killed us a hundred years ago(that said I am aware that antibiotic resistence in bacteria is becoming an incredible problem). Medicine allows babies that would have died at birth to survive and people with congenital conditions to live far longer than they would have without medical intervention. The western worlds way of living is unstainable in the long run in terms of energy requirements and resources but how many people know that. How rediculous it is that people claim somethings unnatural and therefore wrong. The funny thing is that homosexuality happens in other species outside of humans in nature which indicates that it's probably more natural than you're willing to admit.
If you believe it's a choice ask yourself why you believe that? Most people will tell you they are naturally oriented one way or the other if you feel as though you could choose to be sexually aroused by either *** or even both perhaps you're gay or bisexual.