Even if someone makes the point that it's less than 50% because of people "being given religion and them deciding to embrace God," the groups of non-religious still tend to have rates of homosexuality consistent with Christian cultures. If they say that even people who haven't been given God know the difference between right and wrong (then what point does Christianity serve), bring up that animals also tend to have rates of homosexuality well under 50%. If they argue it is a disorder, ask them if baldness or [having whatever color hair, eyes, or whatever superficial body feature they have that doesn't happen to lead to a controversial topic] -- if they mention a real disorder (like obesity, heart disease), remind them that these things pose observable health difficulties -- if they mention anal tearing, mention there can be vaginal tearing. If they mention "sex not being used for procreation," ask them about "Christian" couples that have sex after they turn 45, or that use any contraception (even the "rhythm" method is still a means of contraception). If they talk about "sex outside of marriage," remind them that it's their fault for not allowing gays to marry. If they say that same-sex marriage is wrong, get them to say homosexuality is wrong, and refer them back to step 1.