Witches? 20-25 US total (five of those died in prison). Big deal, yes, but numerically insignificant.
Crusades? Began to reacquire access to the Holy Lands that the Muslims shut off. Maybe one million INCLUDING Christians, Muslims, Jews, and those who died of disease.
The Americas? You figure it out. Note that the priests took the side of the natives against the ruling hierarchy of bishops and the king. Who were the real Christians? The estimate that I saw was 15 million.
So make it 20 million total even if you blame it all as being in the name of Christ (which it wasn't).
Let's add these non-Christian pagan/atheist statists
Genghis Kahn - 40 million
Ming Dynasty fall - 25 million
Timur Lenk - 17 million
An Lushan Revolt - 13 million
Xin Dynasty - 10 million
Yuan Dynasty - 7.5 million
And then abortion (July 2013 figures):
US - total to date 50 million (1.06 million in 2011, and some states (CA) do not report).
World - 40-50 million EVERY YEAR, or 125,000 per day (US >3000 per day). As I write this, the count is 30,669,nnn.
Your "astronomical number" is on the side of the atheists and pagans.
Now, before you get too excited, remember that those with any kind of religion at all would not self-profess to be atheists, but atheist rulers would claim to be religious to fool their subjects.