The other dimension to the stigma of laid-off people is the fact that anytime the whiff of impending lay-off starts floating through the office, people GTFO as soon as possible. Usually these are valuable people in the prime of their careers who won't tolerate even a small probability of getting laid off.

That's bad for everyone including employers, but especially careerists who need an unbroken chain of employment, because yes, even if you're not laid off there's a stigma to "job-hopping" as well.