In Atlanta, even if you observe all the rules, wear a helmet, use bike lights, wear reflecting clothing, you are more likely to get hit by a car than not; or atleast you might know someone who has been through it. I'm basing my assumptions that Boston is like Atlanta (aka terrible public transit, everything is far away, college campuses are in the middle of the city).

On college campuses (like Georgia Tech) a lot of bikers who are college students ignored traffic stops, rules of the road and signals. So it is likely that people from poor households are also equally or more likely to ignore traffic laws.

Also, lots of roads don't have bike lanes, and riding in the middle of the street is going to get you a lot of honking, stuff thrown at you by rude drivers over-taking you, etc (from personal experience).

On another note, London, a city whose mayor is a vocal proponent of making London bike friendly, has had many fatalities that were bike riders following the rules so this risk for fatality is a very real problem.