How can we encourage atheists to peacefully coexist with those who don't agree with them. I mean, atheistic communism was responsible for more deaths than nazism in the 20th century. And although communism was responsible for deaths even on religious grounds, more of those deaths were less about beliefs and more about political power, religion was an excuse.
Who told you so? Have you lived in a Communist country? In the Soviet Union, at least, religious persecution was very much 'about belief' and not about politics. Most Russian Orthodox believers did not engage in any sort of political activism, in fact, most of them tried to peacefully coexist with the Soviet authorities. But from 1917 to the moment when the USSR was involved in World War II, they were ruthlessly persecuted. Just for practising their religion, nothing else. Most priests, monks and nuns were killed, the rest went through prisons, concentration camps and/or exiles. Their children were encouraged to officially reject their parents (usually through a letter published in a newspaper). Those who didn't, were denied higher education, good jobs, they were mocked and ostracised, often imprisoned. Stalin officially proclaimed that ALL
forms of religion (and not only those which presented some political danger) would be eliminated in the USSR in the course of the 'Godless five-year plan'. Only when Nazi Germany threatened the existence of the country, did the authorities weaken their persecution of the Church. And the Church fully supported the fight against German invaders.
After the war, the State allowed the Orthodox Church and most other communities to exist, but only just, demanding in exchange their full political loyalty (which was duly provided). None the less, the Church (and all other religious communities) were subject to all sorts of limitations and humiliations. They were allowed to conduct church services, to print a very limited number of religious books and reviews. But no religious organisation was allowed to do any missionary work, to carry out any charity activities, to hold or participate in any cultural events. Religious books could be sold only in churches or monasteries (of which only few existed). To buy a Bible was a big problem.
Government agents closely watched parish life. Members of the party or their families were not allowed to participate in any religious activities. If they did it on the sly, they were reported and had very big difficulties. All children in the country were expected to join the organisation of young pioneers which subscribed to the ideology of atheism. Those children who refused to do so for religious reasons were harassed by teachers and authorities, their parents - too. Any young man or woman who wanted to have a good higher education or any sort of career had to join the Komsomol - the Young Communist League, which was also atheist. If a Komsomol member was discovered to be religious, he or she was thrown away from the Komsomol, his or her university, lost his or her nice job. His or her parents were also harassed.
Children of priests often were treated as pariahs, encouraged to leave their parents.
Official propaganda always mocked religion - any religion, but most of all - the Orthodox Church, which was considered the most dangerous ideological enemy.
And only very few members of the Church took part in any sort of dissident political activity.