> Just taxing leaded fuel more wouldn't have made the transition as quick; [..]
What makes you think so?
You don't have to get rid of leaded fuel completely to get most of the benefits. If you get rid of 99.99% of leaded fuel, you reap approximately 99.99% of the benefits.
And in fact, leaded fuels aren't banned for all applications. So whatever benefits we have gained, we have gained with some leaded fuels still being in use.
Btw, we allow deadly externalities all the time. Driving your car, whether ICE or electric, at all is a stochastically deadly externality for pedestrians and cyclists and other drivers. See https://en.wikipedia.org/wiki/Acid_Rain_Program for a successful program of trading in externalities.
Why is lead or CO2 from cars special? We still allow lead from some other engines, and we allow lead in eg solder and other applications. Wouldn't it be more efficient to have a uniform tax on its emission into the environment, instead of a ad-hoc patchwork of bans?
> [...] just taxing ICEs more won't force manufacturers to switch to electric and hybrid models quick enough. The threat of a ban will.
How quick is quick enough? And why wouldn't a high enough tax do that? If you tax carbon emissions high enough that ICEs effectively cost an extra millions dollars to run, wouldn't that effectively have the same effects as a ban? (A handfull of billionaires might still run some ICEs for fun, even at those punitive taxes. But they are a rounding error.)
In any case, my point was more aimed at making the life of polluters harder, instead of giving subsidies to electric cars. In my view, a tax on emissions is best, but a ban on ICEs is still better than a subsidy or an explicit mandate for electric cars. That way you don't distort the decisions between riding your pushbike vs moving close to work vs riding an electric car.