I always considered myself agnostic leaning atheist. I consider leftism to be antithetical towards religion. All religions have a class structure to them, do priests, rabbis, or imams not exist? And what about marxism, is karl marx not venerated by some leftists in a weird atheist sort of way?
I'm an atheist but I think it's easier to imagine a post-capitalist society than a post-religious one. I also don't see a point in fighting it.
In the US we have the mantra "separation of church and state" baked into our civic religion, but I think a lot of people misinterpret this and reduce it to "the church is a corrupting influence on the state." As creepy as it is for the state to be making decisions based on theocratic doctrine, I think a lot of people miss just how often this works the other way around - where the state is a corrupting influence on religion and state doctrine becomes the "word of God."
Large denominations have been effectively turned into political machines. Instead of being subject to critical analysis, the holy texts become Rorschach inkblots interpreted from on high in whichever way is most expedient to perpetuating the current manifestation of class society. People in more secular fields like academia or science may thumb their noses at religion, but this corruption of religion is clearly systemic and the same systemic forces are working to turn academia and science into bulwarks of class society as well.