Because if it an illness, it might be fixable or prevented
Normal vs not normal line of thought gets him in trouble.
But if it is an illness, he can claim he simply wants sick people to get better as a rationalization for simply wanting to oppress those that make him uncomfortable.
Here, I'll run with it. There are all kinds of genetic variations that may end up being harmful to the individual, while being beneficial to the population at large. Like sickle cell anemia, which protects against malaria.
In this case (the "gay" gene (or groupings which tend toward it)), a portion of the population has ended up with genes that may be individually harmful (assholes abuse them because they carry this trait), while also being beneficial to society in general (it allows the rest of us to identify the assholes).
