Parade squatters can be a big headache. There's no answer except to be positioned right at the rope or curb and don't leave your spot.
People operating strollers and
ECVs shouldn't be automatically labeled as operating their equipment aggressively. You admit it's hard for you to stop suddenly if someone in front of you stops unexpectedly. Some goes for someone with a stroller or
ECV. Only, they take an extra moment to stop, because they carry an item of weight. Sure, we've all read about the rare jerks. The rest of them, visitors just like you, who are just trying to mind their business and navigate the crowds, are only accidentally touching someone. Blame it on crowded conditions, not bad intentions.
I would not lose your faith in humanity. If crowded times are the only times you can visit WDW, concentrate on the great memories of your vacation and accept that people are going to be bumping into one another. The line cutters and parade squatters, know it's going to happen (unfortunately). Defend yourself if possible, but be ready to lose the game. That's what it is to these people, after all -- a game.