Where do you think the Christians who used to live in North Africa, the former Byzantine empire, the Middle East, Persia, etc. all went?
Yes, the Communists were definitely an evil empire, and their technical capabilities (what they didn't steal from us) came out of their Western heritage. But one thing sets an atheist Communist above an Islamic suicide bomber - the atheist at least wants to preserve his own life, even if he holds the lives of his enemies valueless. So there's a kernel of sanity there not found in radical Islam.
Communism has it's useful idiots and willing fanatics also. Just as Islam's leaders and mullahs never deign to be suicide bombers themselves. They get other saps to do it for them.
Regarding the dead Christians in the Islamic world, yes, that's a lot of dead people. But more of them have either emigrated to the West or converted to Islam for safety. The body count doesn't come close to the Marxist death totals.