YES being an atheist interferes with being moral, for to him there are NO consequences for immorality! And without the ABSOLUTE goodness of God as a reference point, there is no way to judge good from evil, any more than one can say that red is a “better” or more “moral” color than blue.
“Religion is the opium of the people” — turning this quote around, most of us would say that Communism was the opium of the people. It pacified and subjugated millions of people even to their own deaths as they were being marched off to the re-education caps or being starved to death under Mao.