I don't disagree, I think we ALL need to be a little more tolerant. But on the flip side. Letting a child be rude and inconsiderate of others space, is worse than someone being intolerant of that child's rude behavior. As a parent, you should be teaching that child that kicking others seats, being loud on planes, screaming in restaurants, etc... is rude and that is behavior that should stop. Allowing a child to act out and doing nothing and just "tolerating" it is going to manifest itself in different forms as the child gets older. And as they get older, they become MUCH harder to deal with if you haven't taught them respect before the age of 8. I've got a 14 year old. The shit you have to deal with then trumps the shit I had to deal with 5 years ago. It would be so much harder if he thought he was a little king and should do what ever he pleases.
I was in a flight last summer where the kid was a pain in the ass!! Sat across the isle from me. He was loud, cried a lot and wouldn't sit down. However, it didn't bother me that much because he was a little kid, maybe 3 or so, and his parents were trying really hard to get the child to calm down. Not all kids are angels and it was apparent that the parents weren't neglecting his bad behavior. But the parents that allow it annoy the shit out of me... and as for babies. Fuck, there's nothin' you can do. If they cry, you can't just tell a baby to stop. So be a bit tolerant of that.