Eh... for the ones saying they want to adopt, they can't have children on their own. They're desperate for a child to complete their families. It's as much about status as it is about love. You don't get social status without the kids.
I spent the latter half of my childhood in a deeply Evangelical community without being a part of it. The ones who can have families of their own, it's different. It's still about status. And they love their kids. But they love that status too. The children are as much a ticket to heaven and a tool for status as someone to love. They definitely see their kids as property in a sense, and a crop for Jesus.
I don't know that I would say they can't imagine not wanting children so much as I would say they can't imagine refusing to garden for Christ's army.
The kids know it too. There's a reason why so many preacher's kids are so messed up, why they struggle in adulthood, and why they tend to have such high rates of addiction and suicide. The entire patenting ideology of fundamentalist Christianity is spiritually abusive. It's often emotionally and physically abusive as well.
Do you really love your children if you break them? So Jesus will have more souls to fight the war against evil?
The street we lived on, there were two kids who were preacher's kids. One family was a fundamentalist and the other was some kind of Baptist. They each had one child. In the fundie family the kid grew up and became an addict. She had OD'd twice last I heard anything about her. That was years ago. No one has heard anything about her for years. She's kind of off the grid. In the Baptist family, the son killed himself shortly after graduation. They lived right across the street from us. I still remember the shot and his mother's scream.
I also remember a lot of the kinds of pressure and crazy kind of scrutiny those kids were under. My siblings and I played with them some as kids. We heard things, you know? We saw the bruises (mostly emotional) and the hollowed eyes. The sadness.