^Trek often depicts non-human races as being uniform in their behavior, attitudes, and beliefs. It's not due to bad writing so much as it is limited time to adequately present a species. I think most people know there are non-religious Bajorans just as they know there are dishonorable Klingons and trustworthy Romulans.
It's more than just limited time. Aliens in Trek often serve the same purpose as the different peoples that Gulliver encounters in Gulliver's travels. They explore a single socio-political idea that is extracted out of the diversity of humanity, concentrated, and taken to its logical extreme. It therefore acts as a lens where we can see various what-if scenarios, at least how the writer would like us to think of those what-ifs.
If every alien species were as diverse as humanity, it might be more realistic, in a way, but less useful as a storytelling