If my employer tells me to call a person and tell them they are fired because they did a bad job, but it's clear that this is not the reason, I would say: sorry, but I'm not going to do that. Remember, it's an "employer", not a "boss".
(But for what it's worth, this doesn't seem to me like a cut and dry description of what happened here; sales is a very cut-throat quota sensitive profession in my experience.)
But nevertheless, I empathize with people who also have to figure out how to put food on their own family's table, in a profession (HR) that is itself very sensitive to downturns.
The comments in this thread read to me like software developers who have not faced a world where it is not easy get a better new job easily after quitting one that sucks, and / or who are young and unattached with very few expenses, and struggle to put themselves in the shoes of someone for whom a principled resignation could have devastating consequences.
It just seems to me like a classic case of shooting the messenger.
In this case, it's not clear that this isn't the reason. That's something the laidoff employee calls out herself; the HR people aren't familiar with her KPIs or work. They don't have any expertise in her industry, and it's unreasonable to expect that.