It’s a bit of a hypothetical question, because governments always intervene on behalf of the rich and powerful, typically because the government are the rich and powerful. It’s a reliable human constant throughout history.
Consider some early industrialist dumping (say) heavy metals into a waterway, or a gold-mining corporation in some African fleapit dumping cyanide, or an aluminium processor creating lagoons of red mud. If the locals were left to their own devices, it would only be a matter of time before said industrialist ended up floating face down in his own lagoon. Expropriation of public property - in this case a body of water - has often been technically illegal at various times and places, but this obvious violation (no need to invoke the specifics of ‘pollution’) goes curiously unenforced.
Governments collect tax from polluters. Lots of tax. That tax can fund physical protection, plus laws that make whatever-they’re-doing perfectly legal.
I can give you a couple of examples from farming and food policies, since I’m most familiar with those:
Antibiotics are routinely given to farm animals in the US, and were dosed similarly in Europe until fairly recently. This is astoundingly dangerous, as any doctor will tell you. It’s also illegal, or at least it would be if farmers were not exempted from (perfectly good) rules about who is allowed to distribute, buy, and administer antibiotics. The reason they’re exempted from these rules is that they’re also exempted from animal-welfare laws, which apply to every citizen except farmers. They are therefore free to crowd animals into conditions so vile and unsanitary that disease epidemics are inevitable … or would be if they weren’t dosed up with antibiotics. As I understand it, the letter of the law in the US actually does not formally exempt farmers from compliance with rules for pharmaceuticals: it’s just that everyone, all the way down the chain, turns a blind eye.
In the US, animals are fed repartitioning agents so that they can (a) grow very fast and (b) produce more lean meat and less fat. Human bodybuilders who take the same drugs are likely to end up in jail, but farmers are allowed to do it because (a) their animals would die of disease before slaughter if they weren’t forced to grow at unnatural rates and (b) the government has convinced the entire population that they should eat more wheat and soy (good news for wheat and soy farmers) and less saturated fat. Back in the old days when people were happily eating lard and butter, this whole house of cards would have seemed laughable.
Here’s a fascinating (to me) example from the era of The Great Stink (disease and general disgustingness brought about by the habit of throwing sewage into the river). Up until that time, there had been two competing systems: 1) cover it with dirt or 2) throw it in the drinking-water supply. It’s odd that people didn’t consider (2) to be unpleasant even in the absence of germ theory, but people are like that. Anyway, the mid-1800s was the Betamax-vs-VHS turning point for sewage, because that’s when the British government spent a yuuuuge chunk of tax revenue on a new plumbing system for London, which enabled them to … dump the shit into a different place in the river.
Meanwhile, people like Henry Moule were vigorously promoting the ecologically-sound alternative, and it was a fairly close-run thing. Given a decade or two, there would undoubtedly have been enterprising folk setting up earth-supply and compost-removal services, which might even have been free (given that compost has monetary value). The design of the ‘earth closets’ would have evolved into something like elegance. But when the government picks a horse, that horse always wins. And here we are with flush toilets and all the associated costs and problems.
I have a whole bunch of similar examples which fall into one of two categories:
a) harmless things being made illegal so that harmful things can be legally promoted
b) governments deciding on, and subsidizing, their preferred ‘winners’.
But they take a lot of typing and you’d lose interest halfway through.