most people are good, regardless of religion or no religion. Some people, often those that rise to power are murderous psychopaths regardless of religion or no religion. I'm not sure if it bears out or not, but it sure "feels" like more people have been killed in the name of religion than in the name of atheism, but I will also say it also "feels" as though more charity and aid work has been done in the religion than in the name of atheism. Much of this has to do with a long and robust history of religion being the dominant paradigm of mankind for the past several thousand years or more. So if most kingdoms, countries, nations, peoples are run by religion, it's only natural that the psychopaths that come to power are more likely to be religious than not. That being said, I think that religion can be used to control a population and therefore is often the best tool of whomever is in power. There is a reason why Martin Luther was such a rebel and disrupter of his days, and it's because in translating the bible so that not just priests could read it took some of the innate power that religion had away from those in charge and gave some of it back to the people. This is not to say that atheists can be controlling and evil, they have been in the past and will be in the future, but it's simply harder to rule this way than through the voice of god. Of course none of that has anything to do with the question at hand, does religion reduce the likelihood of scientific achievement. The answer to this is I think most assuredly yes, and I think that most religious people would also admit this. However, they may make the argument that scientific breakthroughs are not nearly as important as I think they are. To me, the highest levels of science are at the pinnacle of mankind, but someone else may say it's prayer, or charity, or family, or a bunch of other things, all of which a well reasoned argument could be made.
Muslims believe in a book which teaches them to conquer and kill the infidel, athiests simply lack belief in any deity or holy book. So your reasoning is analogous to blaming someone's misdeeds on their lack of belief in Santa Clause. And given the long and bloody history of rulers, who have professed various faiths, what grounds do you even have to speculate that the communist regime would have behaved any better if they had believed in the Bible.