Axiomatic Unicorn said:
And the large trucking company pays much higher amounts of gasoline and tag taxes, which go for paying for the roads. User fees such as this for tangible consumption are completely appropriate. A web designer who produces more than the trucker still must pay more taxes.
You are assuming
1) petrol levies and similar taxes are specifically earmarked for purposes of maintaining roads. AFAIK, this isn't the case in most countries; all taxes go into the general revenue pool, and the pool is divvied up in whichever way is deemed most beneficial.
2) the pattern by which the tax is levied matches the pattern of wear on the roads. Again, AFAIK, this isn't the case. Road wear and tear is dependent not just on than just distance travelled, but also vehicle tonnage. In particular, a large truck will cause a lot more damage to a road than a passenger car, other things being equal.
3) the amount of tax collected via petrol levies and whatnot is sufficient to meet road maintenance purposes. This is clearly not the case; if it were, there would be no need for tolls, for example.
4) the only purpose of government (as it applies to this particular subject) is to maintain the road network. This isn't so; especially with expanding vehicle use, the question of building new roads and encouraging alternative means of transport is an important one.
In general, infrastructure spending is one of the key ways in which the benefits of government accrue more to wealthier people than poorer ones. Sometimes, a way can be found to match taxation exactly with these benefits. Often, such a way cannot be found, or implementing it would be impractical. Until we live in a perfect world where everything can be accounted for and externalities don't exist, it's perfectly reasonable to have a progressive tax system to reflect such realities.
Furthermore, even if we lived in such a perfect world, it might still be reasonable to use a progressive tax system. One of the recognised functions of government (although a rather unfashionable one, in some circles) is wealth redistribution: to minimise the disparity between the rich and the poor. Collecting more tax from the rich is one way of achieving this. This is not intrinsically good or bad; it all depends on your political leanings.