Firing designers for complaining about their unsanitary working conditions is illegal. Firing warehouse workers for complaining about their unsanitary working conditions is illegal. Firing designers and warehouse workers for attempting to organize together is illegal.
Firing designers for talking about someone else's working conditions isn't "one weird trick" for avoiding the law here.
You are a lawyer and are making this claim as someone who is educated in labor law? Or you have a citation to share with us, or something of that nature? Perhaps the chapter and verse of the law that makes this move illegal? Or a case where it was found that workers have the right to publicly comment on other workers' working conditions as long as they work at the same company?
> Under the NLRA, it is illegal for your employer to:
> Fire, demote, or transfer you, or reduce your hours or change your shift, or otherwise take adverse action against you, or threaten to take any of these actions, because you join or support a union, or because you engage in concerted activity for mutual aid and protection, or because you choose not to engage in any such activity.
You can get a basic overview of this topic by googling things like NLRA, NLRB, and protected concerted activity, including very recent examples of how these concepts have applied. They're much broader protections than you think, and Amazon has very clearly broken them. That's why their spokesman is giving out contradictory statements like saying that they allow employees to discuss eachother's working conditions, then firing them for exactly that.
Do not fall into the trap of thinking that "the company has a policy" or "at-will employment" means "you have no legal rights".