Here's some metaphors I use; if it's bogus, someone please crush them.

Imagine a city with a slum. People ask why the police don't clean up the slum. The police know that if they come in and break up the slum, they'll decentralize the crime - better to keep it fenced in, under watchful eyes, than run wild.

I see a lot of people working roughly with the model that religion is an infection. Sometimes atheism is presented as antibiotics, but regardless of what the prescription is, there seems to be an impression that religion is some kind of foreign force, where once religious belief is removed, there has been clean removal, like surgically removing a boil, instead of getting some of the boil while the infection spreads through the bloodstream.

Religion is an easy target, but removing it, I think, has a tendency to take an army in a fortress and turn it into an army of nomadic assassins, everywhere and nowhere, decentralized and pervasive.