1) Many people (me included) have a strong, emotional aversion to the thought of using physical force against a child that has effectively no way to defend themselves. (Needless to say, such emotional reactions say nothing about whether it's actually right or wrong to hit a child .)

Indeed, I don't have any such aversion, and tend to score pretty low on the "emphathize with other human beings" thing. Which probably explains some of my puzzlement :)

2) AFAIK, there are studies indicating that spanking is an ineffective method of discipline. In general, it seems that positive reinforcement has stronger effects than negative. That'd lead to spanking being both useless and needlessly hurtful to the child, and therefore obviously something to be avoided.

I definitively will research the subject more before I have kids :) Overall, I'm dubious about the idea that negative reinforcement (a.k.a. punishment) is fundamentally ineffective, since fines and jail sentences do seem to work as a deterrant.

3) The notion that hitting a child to make them do what you say teaches them that it's okay to use force against others to get what you want.

Depends how it's used. As the guy in psychohistorian's link says, the problem is when the severety of the punishment depends not of what the kid did, but of how the parent feels. If the kid gets spanked when he knows he did something wrong (like lying), he shouldn't interpret it as meaning that "it's okay to use force against others to get what you want."