I think we atheists have the best and only defense against all of it - rationality and evidence. When you force these groups to be held accountable to evidence and reason, it is much harder for them to get away with what they do. That is the reason I put most of my effort into atheism.
This is not to ignore the horrible atrocities which you refer to but I have to point out that the culprit in the Spanish horror, the Roman Catholic Church, is still very much with us in the US today, is still probably the most powerful force against freedom and honesty of our world, still covering up its involvement in numerous other atrocities and wrongdoings which include its support of fascist regimes and the death squads they enabled to murder millions of socialists. I don't think those of us who know its history should let it get away with murder which it has been able to do throughout its history.