Why should censorship be illegal?

The reasoning behind banning censorship is based on history.

When citizens are not free to speak out against the government, the government becomes unaccountable. Then the people in power become disillusioned with their rule, often creating a dissatisfied society. Usually, this becomes a rebellion and causes chaos. The French Revolution and the American Revolution come to mind. Truth is, even when censorship was illegal, anger grew within a society, eventually it leads to beheading a Monarch... or an all-out war. Either way: there's death and destruction.