The first statement is true. The second sort of misses the point. "Fiduciary duty" isn't a moral obligation or a social norm, it's a darwinian thing.
Publicly traded companies are controlled by whoever wants to buy them. If a company has assets that could produce a profit of $N, but it's currently not doing so and only making $M (and its share price reflects the lower revenue), it will be in someone's interest to buy the company and rework its priorities so it makes them more money.
So... the grandparent was effectively right. Over time, all public entities will act to maximize profit.
I was going to point out that you're missing (or intentionally ignoring) the very next piece in that debate series[1] linked at the bottom of your link, which takes the view that this requirement doesn't exist. But it's not a very good-quality piece, which is presumably a function of the article format (short-form debate aimed at unsophisticated readers).
The flipside of that is that I don't think your original linked piece makes much of a case at all either.
“Modern corporate law does not require for-profit corporations to pursue profit at the expense of everything else, and many do not.”
We aren’t talking about corporations, but rather publicly traded companies. As the previous article pointed out you do have an obligation to your shareholders, and that obligation is to somehow act in their best interest.
Certainly the stock market price goes down if you aren’t growing. And prices going down means you’re not doing right by your shareholders.
I’m happy to be wrong here (I hope it’s true) but whether law or not it seems to be an immutable force.
There is no "fiduciary duty", it's just unwitting HN folk pretending to be business savvy.