In an article entitled, "Pro Bono: Doing Well by Doing Good," Kristen C. Limarzi explains why taking pro bono cases is in your enlightened self-interest.
I generally think lowly of lawyers and law students who do not take pro bono cases. If all you care about is money, get an MBA, because you'll get much richer as a businessperson than as a lawyer. However, I also think lowly of such people because they obviously lack direction, motivation, and initiative.
While in law school I worked on cases filed in and argued before the U.S. Supreme Court; I've written a motion that kept a guy off death row; and I wrote a motion that persuaded a state court judge to strike down a state criminal law on first amendment grounds (during jury selection in a criminal case). Why have I done all this? Is it because I'm the shiz nit? No!
It's because anyone will hire you if you work for free. Since you're working for free, people necessarily give you interesting assignments. A paying boss will feel no guilt dropping a pile of rogs on your desk. But everyone knows that no one will answer or propound discovery for free, unless that discovery is related to a very cool case you're handling.
Thus, by not doing pro bono you tell me you're not a very upright person, or a very smart one.