I admit it's a bit speculative, but really does fit the observed phenomenon well. When a god believer tells you to believe in their God. It's a bit like they are offering this figure in their heads to you, that they have come to know and love. And telling them, no, that doesn't exist, and you're wrong. Really is a kind of rejection of God (of their God in their head) and of that person. Reacting emotionally is the obvious response, whereas I've analogized it to becoming upset because I don't believe in bigfoot, but theists don't have a person relationship with bigfoot.
"Hey, do you want to go steady with my God?" -- No. Your God is fake, stupid, doesn't make any sense. Nobody should go steady with that mythological hogwash.
So ofcourse there's definite rejection going on there.
"Hey, do you want to go steady with my God?" -- No. I'm already going steady with MY God.
Understandably, far less animosity there.
It puts things like Julia Sweeney's Letting God of God chapter where she "breaks up with God" in a new light.