I'm 47 years old. That means that I straddle the smoking/non-smoking divide: smoking wasn't half as loathsome when I was a teen. True, anyone with even minimal awareness knew that it was unhealthy, but it didn't garner quite the level of social disapprobation that it does now. I don't smoke, but I don't care that someone does, as long as they do it in their own space. I like masturbation, but public masturbation, not so much. Smoking in public is like jerking off in public, except that Kleenex doesn't work to contain tar and nicotine in quite the way it does to contain spunk. So public masturbation is actually preferable to public smoking, if you look at it logically. Yet we confine public masturbation to orgies, where the consent to being exposed to masturbatory fluids is a de facto understanding. So smoking should be treated likewise: allow it in clearly-designated smoker's bars, or smoker's establishments. Disallow it in others. Problem solved.

There are a lot of couplings which might be unwise due to known genetic risks, but we don't interfere. To interfere because of a familial relationship is absurd. Love conquers all, remember? What it doesn't conquer can be handled via vacuum aspiration or D&C.