Few people who are doing things that will, with a high degree of certainty, result in harm to others for their own profit want others to be publicly pointing those things out.
Painting this as "trash-talking Amazon", however the fired workers' words are phrased, is hugely disingenuous. We're not talking about someone going out there and saying, "Man, Amazon is just such a loser! They're so ugly, their mama dropped them when they were born and wouldn't pick them up!"
Amazon is putting their workers' lives and health in danger, knowingly and deliberately, for their own profit. Anyone who is truthfully bringing the details of this to the public is a whistleblower, and needs to be considered as such and granted the full protection of the law.
Like...you know legality and morality are not the same thing, right?
I'm not saying they're idiots, and I'm not saying companies should fire employees for airing grievances... but publicly reporting on bad things your employer is doing isn't a good idea if you want to keep your job. I'm not sure why that's surprising to anyone, including the people who got fired.
Clearly Amazon is being a bad actor here overall, both in how they've been not caring about their warehouse workers' health, and how they fired these employees for making a stink about it. But, in general, I don't blame a company for firing employees who trash talk them in public. It's just... kinda common sense that this would happen? But in the specific case of a company doing something like Amazon is doing now, I really want there to be legal protections, because employees should feel safe from retaliation if there's something whistleblower-worthy going on.