Neither should the police, but look at the situation in parts of the US.
I appreciate and agree with the principle of your argument, but if everything worked the way it was supposed to, the world wouldn't need the Avengers. It doesn't, and that's due to the failure of those you want put in control of a handful of good people who haven't put a toe out of line, or shown themselves to be motivated by anything other than protecting innocent people regardless of nationality. And also they saved the world from Loki. Without their intervention, the planet would be under his control.