There is a truth defence to libel in the USA but there is no good faith defence. Think about it like a traffic accident, you may not have intended to drive into the other car but you still caused damage. Just because you meant well doesn't absolve you from paying for the damages.
I'm not sure what exactly you mean by "good faith". The legal standard is "actual malice" which means you had to have either known you were wrong or recklessly disregarded being wrong. Just saying something false about a public figure in a way that causes damages is not enough.
