I know you are not a serious type of person to debate with, but if you want to make the claim that
Country A is the greatest force for good.
you must define your terms. What is precisely meant by "greatest", "force", and "good"? It would probably be wise to define "country" as well.
I think you can go ahead and use whatever common dictionary definition you want for any of those words - it won't change the analysis. Oh, except for "country" which I agree is too narrow, which is why I've also used the words "nation" and "civilization." Feel free to use any of them. Also "greatest" does not mean "per capita." (

Rusty). It means "greatest overall" because that's what actually matters when it comes to things like humanitarian aid, scientific achievement, etc.
When defining American Exceptionalism, the most important thing to remember is what it does
not mean - American Perfectionalism (no matter how furiously Rusty wants to prop up that strawman by saying "well that's what people
think it means"). On balance, considering the good and the bad, America is the greatest force for good this world has ever known. This isn't really debateable unless you think that conquering the native americans over a century ago (who were, themselves, conquering each other for centuries), somehow negates all or most of America's contributions to science and humanitarian causes. In which case, well, we'll just have to agree to disagree on that.