While pretty much all employment in the US is "at will" employment, "good faith" is assumed in the system....
Stack Ranking by default is a "bad faith" system, where the employer, will fire people, even though the employees were good performers (if you are in a team of all good performers, it is common place that stack ranking punishes good performers/employees as well).
It is very similar to the "decimation" system that the Roman Army practiced, when a particular unit or legion performed bad or cowardly in battle, one in ten was chosen (via short sticks), and culled to death by their companions. Very brutal, and can't see how it improves morale even if the unit itself is actually performing well. (which stack ranking is, constant decimation). This causes rampant politicking and favoritism to the point that systematic discrimination arises from it.