That is the question, of course. And it by no means follows that if you can't give your baby nicotine you can't give your baby a hamburger. That level of argumentation is not serious. You ask that as if the question of where to draw the line should automatically lead to the conclusion that no line should be drawn.
This is simply a silly rhetorical (as opposed to a logical) defense for those who don't like where the line is being drawn.
As I said, this particular line will be re-drawn every generation as we understand more about what effects various things have on babies in the womb. So I don't know where, precisely, to draw it; I know it should lie somewhere in the gulf between cigarettes and hamburgers.