[cromwellian]

Because it is an externality. Capitalism works when there are property rights. Even educated libertarians admit that that which is not able to be given property rights must be subject to government oversight.

Public safety is an externality. The air and water are externalities.

Private industry can't effectively compete to optimize a cost which is not "priced in". That's the whole point. If you can pollute, damage public safety, et al, it amounts to a free subsidy, you are externalizing costs which should show up in your balance sheet.

It's like people read Ayn Rand, or some cliff notes version of free market capitalism, but don't read any of the deep philosophical economic arguments in the literature, and then parrot slogans around.