what does Thoreau mean to suggest when he compares legislators with people who put obstacles on the railroad

Thoreau complains that it is ligislators who hamper trade and commerse. They do more harm than good. He uses the metaphor of ligistaters blocking railroads instead of letting the process of trade happen.

..and, if one were to judge these men wholly by the effects of their actions, and not partly by their intentions, they would deserve to be classed and punished with those mischievous persons who put obstructions on the railroads.