'just' is doing a lot of heavy lifting. Lead is still in certain common fuels, some paints, and foods to this day.
That said, if you know how to turn any lab-only solution into an economically viable solution, please do — the world has plenty of room for improvement! :D
I think you can make a good argument that collective action helped end slavery, I don't think you can make a good argument that anything other than market forces is bringing us the transition to renewable energy.
Where's lead in that? I don't know. I don't even know if it's the same answer for each of your three uses of lead.
Ozone was easy to get an international agreement to fix, because it already had economic alternatives.
* and if you want to argue semantics over "are economic forces anything other than the de-facto collective action of the agents in the economy?", which I'm sure someone has energy for, but I'm not that someone, so I'll acknowledge it and move on.
> why would I worry if in centuries we are a billion less?
Indeed, this is my position too. Hyperbolic discounting of the future: we don't know what's coming, let the future sort itself out and worry about the next 5 years.
25 years, we might get AI good enough for robot workforce and we can all retire instantly with no need for more kids entering the workforce to replace the pensioners, might get anti-aging and an end to old-age pensions, might get both, might get neither.
(That said, the example I gave was a reduction to, not by, 6.9%; it would be a global population of 552 million).