Up to a point
"That a spanking is a last resort, I think the analogy is a reach but acceptable. How many parents that do spank their children haven't used the threat of this ultimate penalty?"
If you have spanked, and the child knows you might in the future, then there is an implied threat. And that is all the threat that is ever appropriate. You do not explicitly threaten your child with punishment. Kids have plenty of things to be frightened of without being frightened of irrational parents, too.