Actually baby joggers ARE outlawed in nearly all races.
Doesn't stop people from showing up with them and running anyway. (Sounds like the bandit thread) If the race director says "BABY JOGGERS TO THE BACK", then they implicitly OKing their presense and will get their asses sued off and not have insurance coverage if something happens. If they try to forcibly remove them there's a huge scene. The recommendation from the insurance lawyers has been to do everything reasonable to discourage them, but do NOTHING to acknoledge that they're there.
Why someone would endanger their child by running with them in a crowd is beyond me, but I've heard all the "only time I can race, gets the kids outside, couldn't find a sitter, only time I get oral sex, helps me pick up chicks, etc" arguments. They're all hooey, but I'm sure they sound good on Oprah. I think they should report the parents to social services.
The insurance costs make allowing them outrageous at anything but a walk. Most of the Mosey for a Cure events allow them, but they're the only ones with enough dough and no one runs fast there anyway.
I've had a guy push his 4 year old and get pissed when we tried to keep them out of the chute, then demand we take the *kids* bib too. I think baby joggers are a GREAT invention. I've persoanlly chipped in to buy them for several people. They scare the bejezzus out of me when I see them in races. I've seen people not realize that the wheel is next to them and practically fall on the child and in once case tip the whole deal over. In both cases the people were appologetic, not rude like your example, but in both cases two people had their races ruined.
It's not as bad as the mom who had their daughter follow her on a bike, weaving back and forth, or the dad that had two kids try to follow him on roller blades, but it is another example of people being totally oblivious to their surroundings.