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.
I also don't agree on the principle that regulations are "harmful" or "helpful." Rather, you have to define who the regulation harms, and who it helps. For example antitrust enforcement harms shareholders and some employees of very large firms, but it helps many employees and arguably improves the landscape for competition between many smaller firms. So whether a regulation is preferable comes down to values.
In the case of leaded gas, it harms basically everybody, but it helps fuel companies, so it was an easy thing to change.