See also: public sector unions.
Which is entirely the point!
Why should we trust a large monopoly like Google to have workers' best interests at heart when there's no counter-balancing force with the same power (be it a union, or trust-busting arm of the federal government)?
Everyone forgets that Google and Apple already colluded to suppress wages! https://www.npr.org/sections/alltechconsidered/2015/01/16/37...
It's not a situation like Boeing where there's a very limited number of other places that you can take your skills.
That is absolutely going to have a massive systematic effect on compensation.
The "take it or leave it" attitude strongly insinuates that corporations should be allowed dictatorial control over the manner in which work is completed. There are too many examples to point to which demonstrate the b.s. in this line of thinking.
I may be reading too much into what you wrote, but I never understand the libertarian need to reject government and union control but embrace everything corporate. It's plain weird.
The answer is that we shouldn't, but the latter solution is much better than the former.
I will no longer work for places where unions negotiate. I prefer the clear incentives of an employer over the unclear incentives of union negotiators. You never know when they're honestly standing side-by-side with you or when they're just there to pick your pockets.
This probably says as much about the wider society that you live in as it does about the unions.
This society is not a gerontocracy either. There's quite a few 30-somethings in the government.
No organization is inherently good. Unions can be led by bad actors, and that doesn't diminish their overall value. They provide employees with a countervailing force to use against employers who would otherwise be mostly free to squeeze them for every penny, whether via cut wages, unpaid overtime, etc.