Pre-kids, I had been on several long-haul flights with a kid kicking the back of myseat. I glared at the parents on most occasions, and generally got an apology. In some cases the parents really were trying to control the kids, sometimes not. In all cases, *I chose to not lose my cool over it*, even though I was annoyed. On one occasion on my way to France I actually befriended the haggered dad, made friends with the kids, and made the best of the situation.
With my own kid, I've been pretty lucky. My son usually falls asleep as soon as the plane starts to move. We've had occasional crying, but nothing crazy, and most people seem understanding. My son isn't big enough to kick the front seat, but I'm sure he will at some point and I'll do my best to (1) physically prevent it and (2) teach him the importance not to do it.
I understand that some people don't want kids, don't like kids, and don't want to tolerate kids. If that's the way you feel, you mostly have complete control over your life to avoid kids. In airplanes you simply do not, and as many people have pointed out, sometimes kids just lose it despite the best efforts of parents.
Unfortunately, the reality is that you just have to deal with it in the very rare event that a kid actually loses it for an extended period of time. Kids are a part of the public sphere. You can get all bent out of shape, but that's really your own issue of not being able to deal with a congested, restricted public situation that by its very nature means being forced to potentially deal with all sorts of unpleasant situations. And, frankly, someone's inability to deal gracefully is not my problem.