"I see you had ten underperformers that you have kept on. Didn't you know our company is working hard to save money? I've taken the liberty to fire them, consider this your first warning."
Even the best managers will have a hard time trying to convince upper management that people who miss quotas are worth keeping on.
As you say, quotas have already decided many a employees fate. The difference now is the scale at which the lack of human judgement can be applied. Scale can only hurt affected employees; it can never help them.
You seem to have an unshakable belief in the people you have worked for and hired and their ability to treat their low-paid hires fairly. I've personally had that belief burned away by the realities of working in a minimum-wage job.
Are you having a bad day because you're distracted? Too bad, you're receiving a reprimand for not meeting your quota.
Do you need to get up and walk around because your back is sore? Too bad, that's time you should be spending coding.
Are you stuck in the resolution of a problem? Too bad, prepare to be canned for repeatedly missing your quotas.
Time spent refining your tools? Nope, not allocated. Time spent learning? Nope, not allowed. Fixing a security issue unrelated to your code? You missed your quotas. Training the FNG? Sorry, but you didn't meet quota.
I hired you to write code, after all, and if you don't want to do that, I have a few dozen applications on my desk of people who do want to.
On a more meta note - these wristbands and things like them remove all judgement from the equation. Someone recovering from a hurt back is only viewed as unproductive for an extended period of time, and thus someone to fire. No matter what other things they do for the company, or how they performed prior to the injury.