http://www.theatlanticcities.com/commute/2012/01/transit-sta...
In fact, the data shows that if anything, introducing more transit will reduce crime.
Careful. The provision of new or improved public transport facilities often coincides with, or precedes, the gentrification of an area.
I'd hypothesize this is the more significant causal mechanism at play; ne'er-do-wells driven out of an area by higher property prices.
Bayview/HP aren't even that isolated -- the T muni line goes there, along with lots of buses.
At some level it's inconvenient to go anywhere in SF, but Pac Heights isn't too hard to get to by transit. The Marina is low elevation, but separated by some hills, but even that isn't inaccessible.