If that is our criteria for deciding which sorts of things we ought to legislate, then I might remind everyone that this is also the same sort of logic that the left uses to push their agenda against religion (particularly Christianity). They look at the worst examples of people who call themselves Christians (i.e. the murdering, persecuting popes and Reformers of past ages, also people who supported slavery and racial segregation using the Bible, etc.) and think, if we allow these people to continue teaching what they teach then this is the sort of effect it will leave on the population. "And that would be a detriment to them, to society, and to their children, in my opinion." It could almost be verbatim from a person on the left in their views as to why freedom of religious expression ought to be curtailed.
I say this to point out the fact that this is not a valid way to look at matters of morals. Illicit heterosexuality is equally (I think more, simply because it's more common and prevalent) detrimental to people, to society and their children, and yet not too many people are screaming about legal regulations of premarital sex, adultery, divorce, etc. This is the ultimate double-standard and reveals how our thoughts on this subject have gone awry. It is impossible for the societal and familial effects of immoral sex (of any kind) to negated by any sort of law. It has to be chosen on the individual level, one by one. Otherwise, it never works.