I'll admit, mass transit can get groups of people to visit areas they might not otherwise visit. Silver Spring is a good example, with its Red Line and ample bus line service, clientele from Northeast DC flocks to the area regularly. Are we to view this as a bad thing?
Fact of the matter is, kids from Northeast flock to down town Silver Spring because there is nothing to do in a good sized chunk of Northeast. Fortunately, Silver Spring is a very diverse area, and only a minority take issue with "bad city people" impacting their quality of life.
This xenophobic and often racist attitude is, in my opinion, largely counter productive. First of all, transit access does not increase crime. It may relocate some of it, but the fact of the matter is that right now, roads could just as easily connect criminals with whatever hangouts much easier than trains do.
Now, what do we do if crime moves into our lovely Christian
The change is going on right now in Anacostia, Hyattsville, and Capitol Heights.
But if we as a society are going to quarantine "undesirable" people to the "undesirable" parts of town, we are only guaranteeing that they will remain undesirable.
Besides, who gets to decide what is "undesirable"? Perhaps it is undesirable for lower income residents in parts of the region to be required to spend a good portion of their paycheck on an automobile to get to their job. Perhaps it is undesirable for University of Maryland students to trek a mile to the Metro station because the same type of xenophobia kept the train far from the campus.
I've lived in this area my entire life. Let me assure you that as recent as 20 years ago, there were parts of Georgetown that most well intentioned suburbanites wouldn't dream of visiting. While I was in high school in the mid 1990's, Columbia Heights was considered unsafe, and there were was practically nothing to do there. As recent as five years ago, the US Army banned soldiers at Fort Meade to go to Near Southeast unless they had some kind of official business there.
Without transit, U Street probably never would have recovered from the 1968 riots. NoMa would be just a bunch of empty parking lots. The Rosslyn-Ballston corridor would just be a bunch of derelict garages and warehouses. Rockville Pike would look more like Route 1 in Howard County.
So to Saint Louis, I say stand up to the crime there. Force that agenda on anyone wishing to visit the nicer parts of your town. force them to bring that back to East Saint Louis, and eventually it will be a place you might want to go visit. That's what we do here in DC.