In the 20th Century, one complemented the other and they were almost universally found together. 100+ million murders were the direct result. These are documented facts and they are undeniable. They won't be interpreted or wordsmithed away.
Your argument is weak. It took nearly 2000 years for Christianity to cease it's butchering of infidels, and even other Christians -- how many of us feel some level of shame at the way our Christian forebearers treated the Americans found here when they arrived?. Pockets remain today: Ireland, the Balkans. Beyond Christianity, other non-atheists, today, advocate the butchering of other/non-believers: Muslims and Jews/Christians/Hindus; Hindus and Sikhs.
The problem is not rooted in atheism but in liberty, or rather the want of liberty. Butchers of all stripe seek dominion of over others. They are so convinced of the correctness of their position, they are more than willing to practice human sacrifice to achieve it.
The solution is to base society in liberty. It neither requires nor precludes your beliefs.