People who value the importance of everyone receiving a good legal defense - the same types of people who become public defenders.
My older brother was a public defender, he now works at an actual law firm. The life of a public defender is one I would not wish on anyone. One thing that a public defender does NOT do is offer a good legal defense. In fact, the idea of public defender = good legal defense is such a misnomer that it makes me giggle and cry at the same time.
People who become public defenders are either senseless do-gooders (maybe like the person who would donate to this site) or, usually, dudes who cannot get a good legal job out of law school (like my brother). The people who are defended by them are usually un-defendable and the public defender almost always is overloaded by hundreds of other losing cases to mount a good defense.
If you are going to law school and you are thinking that being a public defender is a good choice, I advise you to think again. Public defense is an practice in futility.