The fact is the PIP hasn't put their job in jeopardy, it was their not meeting expectations that put their job in jeopardy. The reality is once you're there, it's (a) probably obvious due to your manager's consistent displeasure and (b) almost impossible to get out of either way because even if the manager is wrong the employer will side with the manager. The PIP itself is, as you say, just procedural backside-covering to paper up a decision that was already made.
> Lack of discussion is concealment.
With that in mind, is it really better to torture an employee with a set of steps you know they won't execute to your satisfaction anyways and dole out false hope? It seems far more humane to let them know it isn't working out and to put their stuff in a box.
I bet my lunch money that an employee is far more likely to shape up and deliver in line with expectations when they aren't afraid each day they walk into the office may be their last. I think this gives employees more chance to succeed, not less. More transparency isn't always beneficial.