See, because without [Captain America] to tell them, these professional law enforcement officers would have had no concept of "evacuating civilians away from where violence is occurring." These people have had no training at all for what to do in the case of, say, a terrorist attack. Why would they? They're just cops working in post-9/11 New York, while Captain America is an unfrozen science experiment from 1942.Remember: only the special people matter. Everyone else is cannon fodder to make the special people sad, or peons to be saved by the amazing powers of the special people.
Even Cracked Is Noticing the Unexamined Assumptions of the Superhero Genre
One of many money quotes in David Wong's The 5 Ugly Lessons Hiding in Every Superhero Movie: