How should I respond to people who think that homosexuality is an immoral or neurotic choice?

I'm straight, but I have many gay friends. From years of experience, I know that they're virtuous and rational people. Moreover, their romantic relationships are not fundamentally different from mine. Also, I'm a strong believer in gay rights, including gay marriage. So what should I do when confronted with seemingly decent people who think that homosexuality is an immoral choice, based in neurosis, or otherwise unhealthy? These people often present their ideas in polite and seemingly respectable ways; they're not just flaming bigots. Yet still I find them appalling, particularly when used to justify denying rights to gays. Should I be more tolerant of such views? How should I express my disagreement?