I've often noticed a certain transformation that happens in
sports fans when they anticipate a victory by one of their
teams. Opposing fans will talk with relish about how their
team will crush the other guy's team. In doing so they are
transfigured into a future victory party. But it's not just
that they WON, but that they beat the other guy's team. Well
"beat" is not the right word. They usually say stuff like,
"kill," or "massacre," or "smash," or "humiliate," or "blow
out of the water,"

Similarly I have seen the faces of religious people light up
when they anticipate the reaction of disbelievers to their
horrible fate in the afterlife. I overheard one guy lustily
saying to a fellow believer, "I'd like to be a fly on the wall
at the last judgment when he finds out what eternity has in
store for him."

In each case they joy of the person is amplified by the
anticipation of future misery and unhappiness of the opposing
person. In each case the current joy is real and intense but
it's only a reaction to an imagined future happening.

I'm sure most exmos have encountered this from believers.

It's a well-known psychological phenomenon. Not sure what the correct term is, but research has shown that dividing a group of people who don't know eachother into two random groups already creates group-think and an us-vs-them mentality.