To the extent that your neighbors believe in false or unprovable things that don’t exist in our tangible reality, that should concern you. This can absolutely lead to horrifying violence, and has repeatedly done so in the past. The good thing about most major organized religions is that they’ve developed (some) guardrails against murdering the non-believers based on the theory that some intangible being requires this of them.
All first principles are unprovable. Theism does not have a monopoly on violence, so I don't see why I should be more concerned about it then anything else.
Because you can't reason with someone who doesn't employ reason. That doesn't mean they won't kill you - it just shuts down one avenue by which you might talk them out of it.
You can't reason about first principles. What first principles someone chooses as their "axioms" doesn't alter their ability to be reasonable. Materialism or empiricism are just as much a random choice for a base principle as deism or theism or many others.
A lot of the evils that the hardcore atheist crowd (Dawkins, Sam Harris, that crowd) ascribes to religion is oftentimes much better understood as imperialism and other purely political ambitions couched in what was the most common first principle of the time. The desire of European kings (including the Pope) to hold Jerusalem and later Constantinople were much better understood as a desire to control trade and expand their territory/influence rather than some deeply seated religious fervor, just for the example of the crusades. And for things like the inquisition, we can see today as well plenty of largely secular demonization and oppression of marginalized groups.
