Between 63 and 68% of Google is owned by households, directly or via funds.
I'm not sure why would it be more fair for a company to be private and owned by its workers, versus being owned by anybody who wants to.
"Anybody who wants to" is precisely the problem -- there's no correlation between a rando's wishes and the health of a project or working environment. You need people with skin in the game, and in the right game.
That's up to regulators to fix.
As an investor a company's duty is towards shareholders.
I think you left out some part of that sentence, it sort of has two subjects? Companies are not investors.
"As an investor, I only care about a company's duty towards shareholders" maybe?
But no, companies are not obligated -- legally or morally -- to be extractive or abusive in pursuit of shareholder's interests. A company can do whatever it wants, can be formed for whatever reason it wants, and shareholders can vote or divest if they don't like it. The whole "a company's only duty is to its shareholders" is a myth that was widely propagated in the 1980s. There's a kernel of truth to it, but it means much less than is commonly understood.