I don't get it. If you just disable barbarians and be nice to other civs, you can play peaceful without much problems. I admit that you have to build some units to discourage other civs declaring war on you. And if you play on Prince or below, defending is really easy if you have ~1 unit per city. So it doesn't force war on you. It's possible to play and win without conquering anything on Emperor, maybe even above, I haven't tried. Civ V had a "always peace" option iirc. I fear that the civ VI AI with its preference of forward settling would be painful on higher difficulty levels with that option enabled. Is there a mod for that already?