I'm not saying unnatural is a good position. It is at least consistent with the attitudes we see. Re the thought experiment. The standard argument is that of b

I'm not saying unnatural is a good position. It is at least consistent with the attitudes we see. Re the thought experiment. The standard argument is that of birth defects, which is obviously avoided. You could point to evolutionary pressures for the taboo also. The thing is, kind of like pedophilia we've drawn a hard line. You could make the argument that someone the day before their 16th birthday is the same as the day after, therefore it's ok. I think the line being clear has more utility than the alternative. In this situation we're being invited to redraw a line, but where to put it? Do we make the getting pregnant illegal? Not being careful enough? So I would keep the line where it is.