Rob:
(1) Christians have certainly committed horrible crimes. However, religion hasn't been the killer you think it is. Except for the Islamic massacres in Central Asia/India and North Africa you simply can't get large % of the global population numbers either, and Tamerlane--who probably killed more than anyone else, probably killed more Moslems than others.
(2) The pocket version of Christian atrocities cited by many, including our President, and to which you refer, isn't regarded as credible by historians anymore. It originated in reformation polemics, was thereafter adopted as part of the Whig view of history and continued to be propagated until the 19th century, but is often simply untrue or vastly overstated. For example modern historians, who have counted the actual victims, think that during the entire course of the Spanish Inquisition, the total number killed was a bit over . . . 3,000. Not even a good afternoon's work for the NKVD or the SS. That doesn't justify it (though the Ottoman massacre at Otranto, which led to its establishment, killed far more), but it does put it in context. Again, I'm not arguing that Christians haven't committed crimes just that the scale of them has been exaggerated, sometimes grossly.
(3) Christians did not forcibly convert/enslave three continents. North America was conquered--which is what people did back then, including the incumbent inhabitants--but its population north of Mexico was small. There was little forcible conversion, even in Mexico (where the majority of inhabitants seem to have sided with the Spanish and voluntarily converted). In South America--which best matches your statement--there was conquest, some forcible conversion, and like in Mexico, some enslavement. (You will find that church authorities constantly exhorted against both forcible conversion and enslavement, largely in vain as to the second). Overall, though, it was a much more nuanced picture than you think. Indians certainly were enslaved in the Spanish silver mines in Peru and their treatment was terrible--but South America is a big continent and much of it was thinly populated at best before the coming of the Spanish.
There was little forcible conversion by Christians in Africa, and almost no actual enslavement. The reason was simple. White Europeans died from the West African fevers so could not capture slaves there. Instead, they bought them from the local chiefs/kings who sold them Generally they were captives taken in war. By contrast, the Moslems were able to operate in Africa (because many were black natives) and did conduct wide spread slave raids there, though normally in East rather than West Africa. That doesn't mean that the slave trade itself wasn't a crime, but it was the Quakers and the Methodists who led the movement that eventually stopped it.
I won't tell you that Christians did not and do no commit crimes--they certainly did and do. But for the most part (note--I only say the most part) those crimes weren't religious in nature but, like most crimes, were committed to gain wealth or power.
And here is where I think I fundamentally disagree with you. You think religion causes people to act badly. I think that we all have it within us to act badly and that Christianity--or to put it more correctly, the Judeo-Christian religious tradition, has--despite all of its failings--done more to get people to stop killing and robbing each other than anything else in history. If you doubt that, compare the native Europeans to their new, non-Europeans neighbors, or the Israelis to their Palestinian neighbors. Both the native Europeans and the Israelis are far less violent, less prone to stealing and more community minded. Despite all its failings it is the Judeo-Christian tradition that said "don't kill/don't steal" and over the millennia that view has gradually sunk in, at least to a certain extent.