They are taking this game a bit too seriously
Every video game story ever.
But also you need to remember the whole "you die in the game, you get trapped in a virtual recreation of reality until your body wasted away" deal. Though, granted, no one on the protag side knows this tidbit, for them it's mostly a sense of justice thing, since they are trying to bring down a terrorist.
And assuming artifact users get to keep their power in fake reality (which is just a guess at this point) it's not too farfetched for one of them to get a god complex out of it.