I can definitely understand that assuming everyone is not a sociopath is very naive. But the reason I say this is inhumane is not about the security implications.
There's a whole plethora of issues around layoffs that are often ignored. I recall looking at Slack's people list constantly to see which accounts were suddenly marked as "deactivated". People I had great relationships with but never exchanged personal emails simply gone. That dread of "what the fuck is happening" and "am I next?" overcoming you. Some people scramble to create sheets with contact information from those who were laid off.
That's absolutely inhumane.
I survived 3 layoffs in the past few years and I can still distinctly remember the awful feeling each of those left me with. I can only imagine how much worse that is for those affected.
We can separate the security parts from the human parts. Companies choose not to do that, for whatever reason that I simply cannot understand. Especially companies with so called "human resources" should be extremely prepared for situations like this, to make sure everyone is actually treated well.
Recently we had that viral video of a person that recorded themselves getting fired with zero reasoning of why. That's the kind of shit that happens with these layoffs. Bad management at its worst.
In short, I agree with you with regards to security implications. But those can be solved with proper access controls and planning. What I don't agree with is everything else around it. Not once I have seen companies laying off people handle this in any manner that I would describe as humane.
We can do better, I don't know why we don't.