You can't let people in and just "make sure" of anything. What are you gonna do, force people apart? What if they fight you on it? Then your security staff is at risk, too. The only way to make sure is not to allow it.
You don't do it because it creates a situation you can't control. The same way armies during a cold war try not to even get within shooting distance, because you don't know when someone's going to do something jumpy or irrational.
You don't do it because it creates a situation you can't control. The same way armies during a cold war try not to even get within shooting distance, because you don't know when someone's going to do something jumpy or irrational.