Religion

Because we don't know what such a Creator actually wants. People then fight over the desires of this inscrutable Creator.

If you then say you are "following Jesus" that provides no better structure, because people can't agree on what Jesus wants, so people then fight over what Jesus wants. Or when a dominant Christian group gets control, it supresses all the others.

Where then comes a firm morality that we don't fight over?

My view is that the Anglo-American secular tradition provides a better narrative(Despite being a political liberal, philosophically I'm a Burkean conservative). We fought over it in the past, and out of those fights came a narrative of individual rights and freedom of conscience. We agree that tolerance for different viewpoints is the best way to get along with each other. But it didn't come out of the Christian tradition because historically, Christians were never very tolerant.

We should also consider that the militant atheism we find in Marxism-Leninism and it's offshoots is also not part of the Anglo-American tradition. So your criticism of those governments misses the mark. There is no militant atheism in our tradition, there is only freedom of conscience.