I think it goes deeper then that. Secularism means complete disconnection of church and state. Having religious symbols on state buildings goes against that. Religious symbols are a form of propaganda in the end.

I would be okay with making an exception for the head scarf. Tbh I don’t really consider it much of a symbol but I understand their reaction to it. I wish we had similar laws where I am, instead my kids get to learn about creationism (I’m just guessing it’s still taught, I don’t actually have kids).