Paying the bill here, not paying the bill there.
As long as I continue to participate, I am contributing. If I pay taxes, they get spent on activities of which I very strongly disapprove. Unlike Thoreau, I don't have the option of going to jail: he didn't have any kids to worry about. If I can't have a real effect within the system, the answer is to have an effect by reducing the system's size and resources, by the only number I can control.