I agree it was poor management to not oversee what was happening.
This is why management does not give advance notice of layoffs. Usually, when a person gets laid off, their first notion of it is a security guard is there to help them fill a box with their personal items and escort them out.
Nobody likes this, but it's the inevitable result of a bad apple now and then. For example, most people aren't thieves, but banks still need security guards because there are thieves.