I just came into the tail end of this discussion; but I saw a few things that stood out.
This is very dependent on where you are. For example, when I lived in Northern California I frequently rode my bicycle on Interstate 5. There are the occasional signs that state that bicycles must use the next exit. In general, I found the interstate section easier, and much safer, to ride than the alternative roads. In Oregon it is normal to see people riding or walking on Interstate 5. It just depends on where you are
That is a truth that conceals an untruth. To make that statement complete you would need to add that taxes on motor fuel provide less than half of the funds needed for repair and maintenance of roads, and almost none of the funds needed for expansion. With that out of the way, people, without regard to means of locomotion, pay for those activated through a variety of other taxes, be it sales, income, property, or some other mechanism.
Here is an article outlining road costs and who pays them. These bullet points are from the article:
Back to the point made at the beginning of this thread. You make a good point about the difference being that full use of autos relies on the use of public resources. I am concerned with that point because of the desire to push all firearms related "costs" (i.e. criminal behaviour) onto lawful gun owners while refusing to examine and calculate the public benefit.