The problem is when you try to force your religion on everybody else.
Which religion does by existing. Everyone gets to vote. And as long a religions exist, some will do so based on things that are not real.
Additionally, respecting different ways of life, and being religious, are mutually exclusive concepts.
Someone that can genuinely think the way I live my life leads to eternal damnation, and also respect my right to choose, is not a good person. To merely treat others decently, the religious must reconcile internal moral beliefs in ways no-one should have to.
Non-secular thinking is not compatible with a secular utopia on earth. And I'm not talking about horoscopes. But religion, which by definition, is a set of rules for how society should work and how people should live. Often applied on the pain of death, or worse.
Pushing those rules on non-conformers is a intrinsic systemic component. Religion without it is not religion. It's just a nice idea, which subscribers get to hold dear while somehow accepting that anyone who doesn't must inevitably rot in hell, and they have to be ok with that.