The irrationality is more on the upside: tech stocks whose fundamentals make little sense you suspect will go up in value in the short term anyway because of FOMO. A lot of people have made fortunes on those kind of bets, and there are definitely people day trading WSB hyped stocks who don't forget to sell.
You also have some legal rights as a shareholder. I don't know about the US, but for example in my country there is a LEGAL requirement for companies to maximize shareholder value. Few people seem to know when they blame capitalist greed, when really it is a government law. So you can sue the company if you think they mismanage their assets.
Of course there are ways for companies to rip off shareholders. I think there is an old Philip Greenspun article about it, iirc he mentions buying expensive furniture and artwork for the offices.
I suppose it is part of the due dilligence before investing in a company, to check how they spend their money.
But as a stock holder even of a public company, your shares can get diluted to smithereens when they issue new shares to raise money.
For a laugh check out the chart of Helios and Matheson, the MoviePass company that had a fly by night stock spotlight experience a couple of years ago. It's so diluted, the historical price looks like the stock was worth bazillions in the past chart numbers.
There are limits - I would assume the SEC has the ability to approve or deny new issuance of shares. If you have 1 million outstanding shares, they would probably frown upon a filing to issue 1 billion more shares.
Pensions are terrible (at least based on performance so far). Not only do they provide worse returns, many are incentivized to lock you into a specific company for many years.
An friend of mine retired in 2013 and had pensions from the first 3/4 of his career and a 401k from the last 1/4. The 401k grew so much it paid out more than all of the pensions together when annuitized (even with garbage interest rates).
I have a pension and if I maxed out a 401k it would grow "bigger" but that means I'd be saving more than the pension plan payments that come from my salary require me to save.
- there was no individual selection in pension investment. They are risk averse so you end up with bullshit total market stuff that gets tepid gains compared to US stocks.
- it’s impacted by the performance of the company. Many pensions invested part of the money into their own stock/industry so a downturn would impact both job prospects and the pension performance
Pensions are “I know better than thee” bullshit run by a company with some kind of elected moron deciding what happens with your retirement. No thanks
As for the usefulness question: providing liquidity is useful. If an investor considers investing in some project, it helps his decision making if they can be reasonably sure that they will be able to sell their shares later on.
And even if it wasn't useful, why would you care what other people do with their money?