I had a lot of difficulty replying to your comment. I feel intuitively that it's wrong, but it's hard to articulate why.
I guess there are a couple of problems:
a) ambition often drives both good and harmful behavior. Because of this, I feel that ambition is morally neutral.
b) I rankle at the notion that people can be "better" than one another, except in extreme circumstances. Is Mark Zuckerberg better for inventing Facebook, or is my dad better for making a career of healing people's marriages and personal problems through psychotherapy? My dad likes what he does, and is successful, but those who know him would not describe him as ambitious per se. Personally, I believe that Mark Zuckerberg and my father do what they do for their own reasons, and not out of altruism or a desire to make a better world. Or maybe they both do what they do out of a desire to make a better world. I don't think either of them is better than the other.