Turning "environmental regulation" into a unified bloc that must be either supported or opposed in totality is a manipulative political maneuver and it should be forcefully rejected.
Regulations are not people, and they don't have rights. It is fair and reasonable to demand that environmental regulation justify its existence with hard, scientifically verifiable data or else get chopped. Clearly, banning leaded gasoline has that kind of justification, and therefore I'm strongly in favor of maintaining that ban and extending it wherever it isn't in place yet. The same reasonable standard should be applied to other regulations across the board.
It's like saying that some people are dangerous criminals who need to be locked up, and other people are upstanding citizens who should be free to live their lives. Everybody would agree with this. The disagreement is in how you sort people. What category encompasses someone who belongs to the opposing political party? That sort of thing.
Regulation should definitely be justified by scientific data. Who gets to determine what's enough? Who gets to determine what counts? Leaded gasoline is a great example. It was pretty well understood when it was introduced that lead was hazardous and dumping a bunch of it into the atmosphere was unwise. But this was evaded, denied, and suppressed for decades.
Even today, it's not settled. Lead is still used in aviation gasoline in the US. It's being phased out, but it's been in the process of phasing out for a couple of decades and there seems to be no urgency in it.
You'll find plenty of people disagreeing with pretty clearly beneficial environmental regulations because in their view those regulations are not supported by the data. They would completely agree with your statement, while saying that pollution from coal power plants is no big deal, climate change is a myth, etc.
They just published a draft version of the transition plan here: https://www.faa.gov/aircraft/draft_docs/draft_unleaded_avgas...
The FAA started looking at it 14 years ago. They planned to finish phasing it out in 2023. Three years after that, leaded avgas remains ubiquitous, and there's a plan to finish phasing it out in six years. (The 2030 date excludes Alaska, which is planned for 2032.) That's not what urgency looks like.
They started looking at it 14 years ago, but there's been tons of bureaucratic roadblocks that have impeded progress. (Depending on who you ask, the petroleum companies were responsible for some of these.)
Even today, there are reports that the new unleaded avgas formulations cause engine damage, and we don't entirely know why that's happening. So there's still technical issues to work out. (But it's important, so folks are trying to solve them as quickly as possible.)