Not in management so I can't argue with you on that. But it seems like at the time the PIP is summoned, the person has somehow made to fireable-grounds.

I think the PIP is hated because it ruins the illusion of camaraderie, like an ultimatum in marriage. But really, unlike a marriage you shouldn't have that illusion in the first place, you were always a replaceable cog whose only value is what service you can do for your boss. If you always had that perspective then the PIP can be seen as a helpful encouragement to improve rather than a precursor to an actual firing.

There might be a selection bias at hand only people that fail a pip and are fired are eventually free from nda.