It would be more accurate to understand that they have "this problem".
Whatever argument can be made for homosexuality must start with the admission that it is, in fact, abnormal behavior.
Lots of things are not usual. Political activism is not normal and yet here we both are.
Homosexuality is undesirable for a parent to see their child engaging in such behaviors because it very likely precludes the chance of genetic descendants. Then again, we run into a cultural thing here since homosexuals have entered into heterosexual marriages, had children in the past both recent and ancient, just as they seem to do in this film--I have not seen it.
You can either take a hands-off view regarding your fellow Americans liberty or you can call for (questionably successful) reeducation of homosexuals. Reading into your views, it would seem more reasonable for you to want homosexuals to stay with their own kind (e.g. courtship and homosexual unions) rather than to enter into "false" heterosexual marriages and reproduce.