We're pointing out that the problem is not particularly American, this is not a defense. Trying to make America seem worse then most of the world is warping the reality of the problem.
Enslavement and mistreatment is a problem that many cultures, countries and creeds have struggled with. Not admitting this and factoring this into your explanations shows some bias against America.
I am not trying to make it look worse, I am stating that its factual history is very problematic. There were many victims that came out of that history, and still exist to this day. Again, you sound like you're saying "stop picking on America, other people were bad too". That's little comfort to America's victims.
Enslavement and mistreatment is a problem that many cultures, countries and creeds have struggled with. Not admitting this and factoring this into your explanations shows some bias against America.