People who loiter and don't do missions are for the most part people who don't want to play missions and won't play missions for X reason.
So, if you have them in the district, goofing around and have fun, show to the community this game can still be fun, because as we all know, it hasn't the best of reputation, in fact it's reputation is pretty garbage on every game quoting website.
See it this way, they loiter and have fun, show a good image, or they just won't play the game at all ... in one way or another it won't change the time needed to find opposition.
Those "loiters" are so few they don't even fill up a district, especially on NA. It just doesn't change a thing at all.
Let the people that want to have fun, have fun! weather it is by playing mission, or by loitering around.