Apparently, your answer is to draw no line at all. Anything goes, right? The strong survive; to hell with the rest. I'm just glad I'm not in your family.
And your answer is, as yet, unknown, since you ducked the queston.
Yes, my answer is to draw no line at all, to allow freely consenting adults to do whatever they freely choose. Say it with me now: freedom. I, you see, choose to stand on principle and I do not believe that I have the right to prevent someone from viewing pornography, smoking tobacco, drinking alcohol, eating a Triple Quarter Pounder With Extra Cholesterol, or for that matter guzzling DranoTM if he wants to. It's his body, his life, not mine, and definitely not the government's.
The strong survive; to hell with the rest.
Yes, those who are not "strong" enough to resist subsisting solely on DoritosTM may not survive. And I'm not willing to ban DoritosTM to save them. And to hell with anyone who thinks he has that right.
I'm just glad I'm not in your family.
Likewise.