[graemep]

Untaxed externalities are very different from subsidies. We do not generally tax externalities.

I live in the UK where we pay heavy taxes on fuel and we pay higher taxes on vehicles with higher CO2 emissions.

[bzzzt]

They are not so different: it's the same private/public money dynamic but money flowing in different ways. For consumers it doesn't really matter if it's a tax or 'mandatory levy'. For instance: in the EU it's mandatory to pay for disposal of consumer goods, which is priced in with every purchase. That's as close as a 'disposal tax' as you can get.