I don't think anyone can answer this question with any true honesty. I mean, I believe it's just something you couldn't possibly understand until you're in the position.
The character of Superman has shaped many of the values I hold in my life. I do my best to help people when possible. I try to be forthright, courteous and a good person. But if I were to receive all his powers, do I know for a fact that I'd have it in me to be objective and not misuse my abilities?
I read somewhere early on in this thread that someone would topple some bad dictators, but that's exactly my point. As a person who has ascended to the high echelons of power, would I have the right to interfere with someone else's government? That could potentially alienate people. Instill fear instead of faith. Let's not forget that people's perceptions of what is and isn't a hero is relative.
Say I relegated my ability usage to only stopping disasters (floods, earthquakes, volcano eruptions, or transportation problems like a falling airplane or a sinking boat), would that be enough? Would I attempt to stop crime? If I did that, it's a fine line to walk between being a good Samaritan and a vigilante, at least in the legal sense.
I'd like to think that I'd be wise with my abilities, help people to the best of my abilities. Be the altruistic hero that I admire so much in the comics. Remember, the road to hell is paved with good intentions.