Alot of people don't really do army of zealots or religion well in fiction; they always try to transform them into villans for some reason.
The only one that makes sense is 40k for them to be evil, but the other side is more evil, so they are good, and the fact that they are real world manifestations of their faith in reality, that is big.
My story has religion on it but is gradual, and my goal is to have zealots, but they are normal people just that they have a far stronger willpower to push forward because of their faith; going full crazy is kind of lame in my opinion.
The calm, noble, and brave Zealot doesn't have much screen time like the crazy one these days.