What will you replace Christianity (and indeed Islam, Hinduism etc.) with? Humanism won't do, it provides no simple answers and no in-groups toi belong to.

The vast majority of people are dim-witted and wilfully ignorant. Thnking makes their heads hurt, so they don't do it. They want a nice, safe, cosy group to belong to and somebody to give them simple answers to complicated problems. They want somebody who isn't like them to blame when things go wrong and an excuse to congratulate themselves when things go right.

This is why, however good intentions are at the start, systems invariably become authoritarian, or fall to authoritarian opponents. Freedom means taking responsibility and thinking about your actions and their possible consequences. It means making decisions. Most people don't want that, they can't handle it.