It's a term used by a lot of Christians more than Atheists that I see. Usually in describing someone who dislikes Christianity, but not necessarily other religions. In such form it's a strawman to make atheists seem more extreme then they are, so that they're easier targets. There are anti-theist atheists out there. But I'm not one of them. I just think the bible is full of crap.
Early on in human history religion was useful for explaining things that people did not understand, and as an effective form of social control. I don't much see the need for religion nowadays. I suppose that makes me anti-theist.
Might have replied to this before, but that'll have to pass.
I think it is the reaction to long periods of religious oppression and that it has its uses in modern society as long as religion exists as an institution of power. Not so useful when religion is no longer that and seems to dissipate sometime after that happens.