I find arguments like this a bit silly. I believe that religion has to be confined to personal life, and religious harm has to be reduced through a socialist government, but religious people killing others is an idealist argument. Religious people didn't just kill because of ideals, but rather because of the material reality that gave rise to their religion. I personally believe that religion, like the state, might wither away through socialism, but just like the state, it's about handling class contradictions and engaging through a historical and materialist lens, else we're just being idealistic ourselves. Not only that, but practically speaking many of our comrades are religious, as long as they agree with us on examining society through diamat and commit to reducing religious harm, I don't care if they pray or not. Let their religious views inspire them towards positive change, and influence their own religious communities through organizing.