Every idea is an incitement

Laws against sedition are often justified on the basis that they ban not abstract speech, but "incitement". I think the best response to this was given by US Supreme Court Justice Oliver Wendell Holmes, in his dissent in Gitlow v. People:

Every idea is an incitement. It offers itself for belief, and, if believed, it is acted on unless some other belief outweighs it or some failure of energy stifles the movement at its birth. The only difference between the expression of an opinion and an incitement in the narrower sense is the speaker's enthusiasm for the result.

According to Holmes, only speech which attempted to induce immediate and concrete action (rather than action at some indefinite time in the future) could be dealt with by the law. Anything short of this - in th e case in question, publishing a pamphlet advocating the violent overthrow of all forms of government - did not pose a "clear and present danger" of "substantive evils" justifying intervention.

As for the long-term threat posed by allowing such advocacy, Holmes was quite sanguine:

If, in the long run, the beliefs expressed in proletarian dictatorship are destined to be accepted by the dominant forces of the community, the only meaning of free speech is that they should be given their chance and have their way.

Democracy should stand or fall on its own merits. If it can stand against the best arguments of opposing systems, it does not need legal protection; if it cannot, it does not deserve it. Either way, laws protecting it from criticism or preventing the advocacy of opposing ideologies cannot be justified.