I guess my previous post was not obvious enough. There is only so much explanation you can do in about a hundred words. But even the little clarification in the comment didn't seem to clear it up.
What I learned in economics class was that road taxes should contribute to not only the cost of resurfacing but also towards external costs such as pollution, congestion, noise, and in general any external disruption to those affected by the road.
And comparing lorries with cars, even if we assume that the relative weight on the tarmac is ten to one, the relative weight of knock-on disruption is much more than ten to one.
How often does a shed load from a car close off the entire motorway? How often does a jack-knifed car close all three lanes? There is a certain amount of revenue to be collected, there are arguments for raising or lowering that. But to reflect disruption effects, proportionately the lorry drivers should pay more. Car drivers and other taxpayers should pay proportionately less.
So I do not agree that we'd all end up paying more. It's just redistribution of society's charges to more accurately reflect society's costs.
If it's still unclear, then I can always bring in some maths ;)