Its just not by a law. Its a fund for the government projects and we need to support health care and social services, to provide water and garbage services etc. Because of tax, it will help to ensure the roads you travel on our safe and well-maintained. And the crimes of our country will be reduced because of national defense. They also fund a Public schools to maintain a monopoly on the education of children. That's the other reason why we must pay tax and its a great help to our country.