I suppose it's all more or less a split second kind of decision. No two situations are ever exactly alike so we tend to go with what we feel is the right course of action.

Based on what you wrote above I don't think I would've intervened personally in that sort of scenario. But you never know, folks these days often prefer to sit back and enjoy the show (maybe taking pictures with their iPhone in the process) instead of actively doing something helpful.

Then again, sometimes it is better to stay away. Homeless people, junkies, folks with mental issues etc. often get in trouble but trying to lend a helping hand might easily put you in an unpredictable position, possibly even a physical confrontation. So I can understand why people often prefer to walk away rather than risk getting caught in a messy situation.