I'm not sure your question goes deep enough, however you are right in one respect it is a set up.
I don't know if you have noticed but at times it takes on almost a battle ground logic.
It's not an attempt by anyone to change anyone else's mind it is pure propaganda usually started by one of the more extreme religious groups or sects. They make outrageous claims and statements knowing full well it will automatically generate a response which is the whole point of the exercise. They will then keep it going for as long as possible as a way to draw attention to themselves and whatever outlandish group they represent.
I think one of the newest around here was a bunch who claimed that they could explain and prove everything that has happened not only on Earth but the Universe happened in 6,000 years ! Why 6,000 you may ask, well there is the other group who have back calculated the ages of the Biblical prophets back to Adam and Eve and arrived at that figure.
So from just these two extreme examples you can see why, not just atheists, but any sane thinking individuals are drawn in to defend Logic, Reason and Common Sense.
At one time I thought it was amusing and fun but now they are just plain annoying, childish almost, and all they accomplish is that they degrade the faith they say they are trying to uphold.
No one enjoys a good religious debate more than I, I’m not out to convert or be converted I merely want to understand other people’s beliefs but I will not be brow beaten by twisted nonsensical religious rhetoric at the hands of some lunatic evangelical or fundamentalist moron out for kicks.