it's a useful way to distinguish between people who happen to not have children, and people who have made a conscious decision not to have them at all.

I don't think it's quite as simple as that. The nutcases are choosing to use the term childfree rather than something like childless. The first term implies that children are a burden; the second term implies that children are an asset. When someone chooses one or the other of these terms to describe his/her situation, I'd say that a value judgment is being made.