why do people who profess to have no religion or spirit insist on commenting in religion and spirituality?

Well you religious folks keep asking us question and it would be just rude not to answer!

Simple, we insist on commenting on your beliefs because you propose a truth about the world in which we all live. Theists claim that there is a supreme entity that created everything and controls everything. Since you guys propose this truth to the world and all of it's inhabitants, it is your responsibility to explain the details of this truth. If I claim that I found a cure for cancer, that would be a claim that could change the world. I would then owe the world an explanation on the details of this claim. We atheists do not propose anything, so we don't have to explain anything (although we are always happy to explain anyways). Honestly, is this unfair in any way?!

Because I have an interest in and opinions concerning religion and spirituality.

Because asking religious questions in the cat section makes as much sense as asking biology questions in the religion section.

Because we know about the history of atrocities carried out in the name of religion.

Why do non felines insist on commenting in the cat section?

To question those that do & let them see the errors of their ways. You can lead a horse to water but you can't make it drink.

Just because I have no religion, doesn't mean I don't have an opinion about it.

Someone has to protect the world from you people

As others have said, last time nonbelievers let believers have their way, we had the dark ages