I was referring to those atheists out there who feel some drive to convert the world to atheism, to condemn and discredit theism (and often 'religion' more broadly) and maybe even to make those obscurantist abominations finally disappear. Some become activists in that cause.
We can find similar evangelical personalities among Christians (missionaries almost paradigmatically fit that description), among socialists, or whatever it might happen to be.
My suspicion is that it might have more to do with personality types than with whatever the particular cause is, though some causes do seem to lend themselves to militancy much more than others.
Atheism seems pretty benign in that regard. Christianity has a much worse record. In reality, atheism is probably closer to herding cats than it is to a mass social-change movement.
I've never encountered an atheist who made it their business to convert people to atheism. Condemning and discrediting theism isn't a mark of militancy, it is (at least in this context) a defense mechanism against the proliferation of religious dogma in society, whether that's government or the creation and enforcement of social taboos.
Nor is being passionate a mark of militancy. I think this is where your confusion lies.