There were many examples where dams weren't built to protect local ecosystems. Pumped storage denied. Roads not build that could shorten the travel. Ethanol in fuel that actually emitted more CO2 because of land use change to satisfy the enforced demand. Multi-use bags that require so much energy and resources to build that you need to use them thousand times to get even with single use ones. Paper bags that require more energy and resources to produce which decay or burn releasing CO2. Plug-in hybrids that barely anyone charges that are hauling useless heavy batteries while burning more gasoline. Whole recycling scam mascarading as a solution. All these dumb specific interventions that backfire.

The only thing that comes to my mind that actually improved situation was the global ban on fluorocarbons.