Because I can, that's why... If you posses the ability to make the world a slightly better place, even if just for a moment, it is your responsibility to do it. The moment I stop doing things because it's the right thing and instead start doing them for the approval I get, is the same moment I lose a bit of myself. I don't know if it is taught or genetic, or both, but the urge to do what is right is not something you can just ignore. If you had the choice to improve the world you live in, or to remain passive; it would be a crime against all that is good to forsake that because you wouldn't get a pat on the back.
Imagine a world, if you can, where all good actions are solely dictated by the recognition they get. That's a scary world, is it not?