Why is it illegal for two consenting adults to fight to the death for entertainment?

Whatever happened to freedom and the sovereignty of the individual? If two individuals are of consenting age and agree to fight to the death and to sign a contract, why is it still illegal in our free and democratic society? Are their lives not their property, or is it the responsibility of the government and they must be jailed for life at the expense of the taxpayer? Then, why do we claim to be a free and open society?