so long as the government DIDN'T use it as a method of extracting more tax
There's the catch. The government need to raise more tax. They can't justify a blatant tax rise because they're not achieving anything with the money so they can't resist the urge to incorporate a little tax hike in everything they meddle with.
Fuel duty is a pretty reasonable tax on vehicle usage. It's easy to enforce, difficult to circumvent and is directly based on choice of vehicle and usage of that vehicle.
Road pricing is a gimmick someone has sold the government with all sorts of promises attached. The fact is, deploying it nationwide would require a large IT system to be commissioned by the government. We know where that'll end. An expensive disaster.
If a city gets a spangly new public transport system that works, congestion charging can be used to locally apply a loading to vehicle use as it does in London, although in practice a decent public transport system will sell itself - not that we've ever seen one in this country.
Of course you could all give up your gas guzzlers and get Smart cars or similar!!
You'd see me driving around on my dad's sit-on mower before I get behind the wheel of a Smart.
Kevin