I think a lot of it has to do with perspective and how the person's day has gone. I read this thread thinking of my own opinions and who I agreed with and who I didn't but the more I thought about it the more I realized I think a lot of it is circumstantial. Most of us start off our DL morning all excitement and glee. You need to join your wife and son who's way up front? Sure, no problem, we all know how bathrooms, etc happen. I don't even have an issue with the FP runner joining back up. I'm usually a "as long as it's only a couple people" regardless of age kind of line person, but then it's 3pm and I've been in line for Space for an hour and 15 minutes and 30 something people have gone in front of me and then I start to get aggravated. I think the same applies to stroller people and I will be the first to say that I wish they did exist but they do and I deal. I think stroller people get to the same point at some point in the day like I do with line cutting/joining. They start off the morning with people running ahead of them but it's no big, they've got all day, but then it's 2pm and another group of teenagers has just cut them off jumping in front of them in line for the Matterhorn.
I too have a "space issue" in lines though. It drives me nuts when people keep bumping into me. A couple times okay, accident, but it gets to a point where I want to turn around and bump back. I understand that there are little ones all around, but if your child has bumped into me over and over and over and I keep looking at you, it's your responsibility to make sure it doesn't happen again. Pick them up,
put them in the stroller, engage their attention. The gal who mentioned that she holds her son is right, if people are standing close enough to her that he kicks them, it is their fault. Toddlers legs are not that long, you should not be so close that they reach you.
I also think some parents need to be more aware of their child's needs. Too many parents these days do not want to be inconvenienced by their own children. If your child is hungry or tired then it's your responsibility to see to that now, not after the Story Book Canal boats when your child has kicked me three times. My niece threw a fit while in line for Dumbo so we left the line. It was no one else's responsibility to see to her, it was mine. I understand you want to get the value of your vacation but if you take a little time to respond to your child it'll go a lot more smoothly for everyone. Obviously this does not apply to everyone but our world in general is becoming more and more about entitlement and less and less about responsibility and that has got to change.