The freedom to distribute ones beliefs is something that the creators of the US were very adamant about. The ability to openly and publicly criticize a governing body was not something afforded under British rule. Speaking out against the King was punishable by death. The creators of the constitution wanted a nation where this criticism was not only allowed, but encouraged. Behind every criticism is an idea of how to do things differently. These suggestions are often not a better solution, but when a better solution presents itself, all of the bad criticism is worth it.
Sedition, while perhaps not the best for the government, should still be a protected free speech class. If the government was to start policing free speech it would start a slippery slope that we do not want to go down. Sedition also can help the government in a way. I think that it can spark reform and move causes.
I think sedition should be protected by free speech for the simple fact that it is speech. I know people are easily manipulated--just look at the reign of dictators like Adolf Hitler--but sometimes we do need to rebel against our governments, and a voice of sedition is needed to ignite it.
Free speech only goes so far to protect someone if they are not hurting another person. Sedition would make it so rebelling is protected free speech, which would only serve to harm people. No matter who the person is, if they're innocent or guilty, they should have the right to be protected from such a thing being free speech.
As much as we may disagree with some forms of sedition, I think it is something that should be protected by free speech. There are examples of speech that should not be protected though like yelling "fire" in a crowded building. But things like sedition is usually very subjective and should not be banned from our abilities as citizens.