Because people have different opinions on morality. Civic duty is not an objective, quantifiable constant. It is a matter of personal opinion, with a great de

Because people have different opinions on morality. Civic duty is not an objective, quantifiable constant. It is a matter of personal opinion, with a great deal of variation, and those sorts of things should not be legislated. If you reduce your tax burden from 30% to 20% using legal avoidance loopholes, and you think that one's moral obligation to support the community ought to be around 10%, that's still another 10% worth of loopholes to find before you'll ever feel like picking up litter at the local park.