I think America is trending up, we are certainly a better global role model now than at any time in history.
America is leading edge when it comes to racism, sexism, and religious intolerance. If you think it is bad here, just go visit one of the other countries. Also look at America's past to see how these groups of people were treated. Now is the best time in history to be someone other than a straight, white, male in america.
Overall the amount of atrocities has gone way down, native americans, slavery, japanese internement camps, etc, and we do not colonize other countries like we used to, Philippines, etc.
We also provide tons of aid to many poor people/countries around the world, with a somewhat ridiculous foreign aid budget.
We are not a white knight yet, however from a global perspective America is better now than we have ever been throughout history.