April 15 -- Tax Day -- has come to symbolize America's lack of economic freedom. Americans have no more claim to their incomes than did medieval serfs. The most successful Americans are comparable to slaves. The long struggle for freedom was a struggle to own oneself and the value of one's labor. European serfs did not own their labor. Consequently, they were not free to sell their labor in markets for wages. In the feudal age, labor, like land, was not bought and sold, but allocated according to a system of use rights. The lord of the manor could claim as much as one-third of a serf's working time. The remainder of the time, serfs would produce for their own households. When serfs became owners of their labor, which they sold for wages, they became free men unaccountable to lords. Freed labor produced independent men because men had nothing to fall back on except their own strivings. A slave was worse off than a serf. A serf faced a maximum tax rate of 33 percent, but a slave was owned by another and had no claim to his own labor beyond subsistence. Low-income Americans face a Social Security and Medicare tax rate of 15.3 percent, a federal income-tax rate of 15 percent, federal excise taxes, state income and sales taxes, and local property taxes. The combined tax rate exceeds the burden borne by a medieval serf. Upper-income Americans are exploited like 19th century slaves. The uncapped Medicare tax places the top federal income-tax rate at 41.5 percent. Adding in Social Security, excise, state income and sales taxes, and property taxes produces a tax burden in excess of 50 percent.