Random family seating anecdote. A couple of years ago, we were on vacation and my wife had to go home early to tend for a sick pet. My daughter and I also re-arranged our flight to get home early, and ended up in like the D boarding group (on Southwest). So we're getting on the plane and we're almost dead last, and there are very few seats left together anywhere. My 6 yr old daughter was not really emotionally equipped to sit alone at that point.

We get about 2/3 of the down and there's now nothing, so I say -- with some desperation -- "If someone would be willing to switch seats so my daughter and I can sit together I'll give you $20." A guy says "I don't want the money but I'll switch."

Which sort of shows that if you're not a jerk, and you ask nicely, often people will go out of their way to help you.

Families who seem to expect other passengers to move, especially when there's assigned seating, are another story, and deserve the condemnation they get, IMHO.