For me it's a combo between this /and/ just people's attitude - it's fine if you want to be slow, but you have to be considerate of others. I wouldn't be mad if you were walking slowly on the side of the street - probably wouldn't even notice - but I'll be mad if you're walking slowly in the middle. It often costs nothing to be considerate, and it makes life more pleasant for everyone!
The problem with PATH is, ironically, pedestrians. My biggest gripe are people walking slowly, 3 or 4 abreast. The list goes on: stopping and turning 180 suddenly, bumping into each other cutting corners etc.
It bothers me enough that I started to fantasize about adopting road-like rules for walking in busy places: no more than 2 persons side to side, no sudden stops, green and red lights in the row of doors to regulate the direction of the flow, cutting corners is only allowed for right turns...