An alternative to atheist thought

[Astonished]

I agree that life matters. I am a a life long old fart, anti-fascist ambulance driving vegetarian. I just don't ascribe agency or purpose to life.

Well put. Not assigning purpose, meaning or agency is not even remotely the same as claiming life doesn't matter.

This is the fundamental error of many, probably most believers: assuming that purpose, meaning, virtue, civility, love and joy can come only from their pet deity. From that, generally, flows a lack of understanding of what unbelief is and isn't, the motivations for it, and the implications of it. And that's being charitable; it's usually not just a lack of understanding but a lack of interest / curiosity / desire to understand. It's far easier to mischaracterize if not outright dehumanize people who aren't impressed with your beliefs, than to even entertain the possibility that they might have an honest point of some kind.

Also, I would ask, what is it that gives their pet deity meaning, purpose, etc., particularly throughout and eternal existence? Passing the buck never fixes the problem.