It is a while since I've looked at the precise figures so this is out of date by some years but the motorist paid somewhere around £36 - £40 billion per year in tax directly relating to motor vehicles - so fuel, tax on new cars etc. A proportion of this was spent on roads and transport and the rest went into the big pot that paid for the NHS etc. It is, therefore, quite clear that motorists are not parasitic in any why but they actually subsidise other areas of society. This ignores the indirect impact of having an effective and efficient road system on the economy such as allowing business to operate, people to travel as tourists to more remote areas sustaining an economy there, people travelling to stalking even.
I am a motorist
and a cyclist, so a parasite from any perspective apparently!
VED and Fuel Duty do generate what sounds like large amounts of revenue, but they are pretty small beer overall in the grand scheme of things.
Here are the numbers from 2017-18.
Fuel duty is about 28 billion, whilst VED (which is under "Other indirect taxes") is around 6 billion. The Government, of course, is pushing us to move away from dirty diesel towards environmentally-efficient electric (ha!) so it is not unreasonable to expect sources of revenue to decline going forwards.
Now if I really wanted to be really provocative I would point to the research that has found that the growth in cyclists is "disproportionately an activity of affluent, white men" (source:
https://researchonline.lshtm.ac.uk/id/eprint/1179/1/Cycling_and_the_city_published_author_copy.pdf). Hence there is also the possibility that these hated MAMIL cyclists are contributing more through areas like VAT, NI and Income Tax than is raised through car-related taxes anyway. Those full carbon bikes don't come cheap!
Of course the truth is that we have no way of knowing, which is exactly why it is so preposterous for any individual, or group of individuals, to lay claim to ownership of tax funded assets, whether roads, hospitals, or whatever. Such assertions frequently operate on the mistaken belief that the population can somehow be divided up into nice discrete groups - for examples "motorists" and "cyclists". In reality there is a huge amount of crossover, and I speak as someone who has paid three lots of expensive VED and thousands in fuel duty over more years than I care to think about.
As the National Travel Survey found, "over four-fifths (83%) of people aged 18 years+ who cycled held a driving licence and drove". So who owns the roads then - the motorist alone, or the motorist who cycles?
See how dumb the whole concept of an argument about "who owns the road" is?