Prove what exactly? Are you telling me that someone actually performed experiments upon people to make them "turn" their sexual orientation? Show it.
A few years ago, "gay" activists asked the Dali Lama what he thought about studies that seemed to indicate that homosexual behavior was hard wired. His response was to ask what came first, the brain's structure or the thinking. In the same vein, OCD patients were taught to modify their thinking so that rather than resisting the compulsion, they should simply observe it and repeat to themselves that it wasn't them doing the deed. Most had a significant improvement in their behavior and brain scans actually showed their brains as having been rewired. This isn't to say some people do not have a propensity for homosexual behavior, but it does prove that the brain and the behavior it initiates is much more malleable than previously thought.
Edit: Oh, I just realized what you said earlier. You seem to also think that humans aren't animals.That we can't know anything about humans by learning about other animals as well, as you don't seem to think that we are animals..
I did not say or imply that at all. All I said is that experts who actually go out into the field to study homosexual behavior in animals are quick to stress that it is a mistake to project human motives into animals. That's not to say we aren't animals ourselves, but only to say that what motivates us does not necessarily motivate other animals. For example, homosexual behavior is very often used to establish dominance or simply to relieve sexual tension with no emotional attachment or self-conscious intent. That's quite different than what we see in humans.
Now, I understand that what this entails might be of great interest and concern to some, but sex, homosexual and heterosexual, holds very little interest for me. I just think that people who debate the issue should get their facts straight and be consistent in the matter.