I think you've misunderstood a very fundamental part of what is being compared. Calling science a religion is comparing apples to oranges. Science is not a faith and will never be.
Science isn't a religion. It's not even a faith. It's a method for finding truth. We all use various methods for finding the truth. "Common sense" is another very popular system for finding the truth. Which options "feels" right is another one. The nice thing with science is that it's pretty well defined so it becomes a bit easier to understand which steps other people took to reach their truth using science. It makes communication easier.
The holocaust and the communist "experiments" have all been done in the name of science. So in numbers of people killed I don't think religion is even close, even though they've had plenty more time to do it. But that's not an argument for religion. It doesn't add to its credibility. All it means is that we shouldn't draw too strong conclusions if we don't have enough material to back our theories up with. That goes for any theory. Religious and secular alike. If we do the right thing for the wrong reason, we aren't less deluded.