Generally they don't involve posting in a place that is actively toxic to you. As for keeping aliens out... yeah, I'm pretty sure a position that requires being able to establish a bond with the locals might not exactly be open to aliens who are so differant they have to go around in environmental suits.You've never heard of cultural exchange programs, have you?
Apparently it's been classified only to you that Starfleet typically employs the mentality that any peaceful and productive species is welcome to Earth.
Starfleet security is generally recognized as being part of Starfleet.Starfleet security used transporters to get to Harry Kim's location when he was under house arrest in a Voyager episode. And that's just off the top of my head. So either Starfleet replaced the police forces or the police forces have been shown to use them. Take your pick.
Compared to having it so if the suit breaks down, he teleports away? Definately.I've heard a mass transportation system that requires maintaining roads, production and maintenance of millions of personal vehicles, driver education facilities, insurance laws/facilities, safety laws/facilities and several other interesting ideas is also a complicated idea.
But yeah, I guess potentially one alien police officer is a bit much, huh?
Honestly, you are concocting an extreme complex explanation for a very simple thing. The simplest explanation is that the suit is to prevent you from dying when you go mach 2 or higher on the motor cycle. This is the future