For employees it is evil a sort of substitute for slaves and indentured servants.
Seriously folks. Let's not for a moment pretend that this is remotely similar to actual slavery. We're talking about two companies to collude to suppress wages for employees that by all objective standards are paid pretty well and have pretty good lives. Are you seriously going to claim that that is in any way comparable to being the property of another human being?
Yes this collusion is wrong. No it isn't even close to slavery. Claiming that the two are anything similar is unbelievably clueless.
Is it that far off really? Many engineers come out of school with 100k+ in debt. They go to work for one of these companies and can never leave because of secret agreements from the execs. Their wages are kept artificially low in a high cost of living area. Between rent/mortgage and other costs of living, they simply can't afford to drop the job and go elsewhere without having another job in the wings.
This isn't much different from indentured servitude. Only with indentured servants there is typically a contract up front, after X number of years you're free to move on. In Silicon Valley its all backroom deals, under the table and out of sight from the public. Your "owners" own you without you explicitly knowing it, there is no end date and there is serious direct career consequences if you try to change it.
They may not be subjected to beatings but they are certainly subject to economic ruin if they try to change or improve their station. I've seen it happen. I've seen good engineers leave engineering altogether because they became untouchable simply because of who they once worked for.