[ZenGum]

It keeps coming up for two reasons.
Firstly, many religions instruct their followers that it is their duty to convert the rest of the world to The Path. Hence they get out and push pamphlets etc.
Secondly, non-religious types find it troubling when religious types get their hands on the levers of power and use those levers to push what the non-religious types consider to be a load of nonsense, and often quite dangerous nonsense.
Conflict is inevitable, but violent conflict is (sometimes) avoidable.