I guess if you want to say it is moral to let everyone have free speech, I could see where you are coming from. I look at it differently, though.
Some laws have moral components, but some are just plain legislating morality. I dont think raising funds for a highway is legislating morality, but I guess some people might.
Perhaps you are confusing laws forcing or restraining certain actions from laws forcing attitudes or forcing people to love others.
To put it simply, we have a house "law" that requires our boys to take out the garbage but this house "law" does nothing to make their hearts change so that they want to take out the garbage.
Likewise, we can create laws that ban certain actions but doing so does not change the underlying nature of the person and just like our boys will find a million excuses to avoid taking the garbage out so laws that force people to adopt a behavior will likely fail because their heart is not in it.
But you forget that the interstate system was proposed under the Eisenhower administration to help in the defense of the country to mobiles troops and supplies. Also, IIRC, originally 1 mile in every 5 was to be straight, so that is could potentially be used as a runway.
Once one builds a road, it is imperative that they maintain it; otherwise you risk injury and death of those who use it.
So highways were partially designed to support self-defense, a moral issue, and their maintenance is to prevent injury and death, also a moral issue.