Actually, I love the XKCD cartoon about free speech. And I do often see it cited for an appropriate purpose -- to explain to someone that getting kicked out of a private, online community is probably not a violation of their free speech rights.
However, it is absolutely not the case that freedom of speech just means the government can't put you in jail for what you say. Here are a few hypotheticals that have nothing to do with putting anyone in jail for what they said that could easily be violations of the right to freedom of speech depending on the specific facts:
A court orders a person not to say something because it might be slanderous, even though there has been no hearing yet on whether it is or isn't slanderous.
A law imposes a $500 per person tax per year and another law offers anyone who doesn't publicly criticize the government a $500 tax rebate.
A court issues an award in a slander case even though the statements made were all factually true.
A securities dealer publishes an article in his blog in which he describes President Obama as a Kenyan Muslim tyrant. Based just on that blog article, the SEC calls the company that employs him and asks what additional monitoring they think is appropriate given that they have a dealer who appears to be unstable. The company says they'll fire the dealer if that will make the SEC happy, and the SEC says that would be swell. The company fires the dealer.
A government tax agency uses different reviewing standards for registration applications from organizations that support Liberal causes than they do for applications from organizations that support Conservative causes.
A public school suspends students who refuse to stop showing their opposition to a war.
A public university allows organizations sponsored by Conservative groups to meet in their facilities but does not allow organizations sponsored by Liberal groups.
A public university changes their mind about hiring a professor after he makes a series of tweets some consider anti-Christian.
Fearing violence in response to a march planned by Nazis, a City requires the Nazis to pay high security fees in order to hold the march.
Fearing possible violence in response to a controversial speech, police remove a person who wishes to speak from a public forum in which he planned to speak, without first even considering the possibility of protecting him or arresting anyone who was actually violent.
And so on.
And so on.
Free speech rights include an lot more than just "the government can't jail you for what you say". I get that a simple mistake might deserve a simple correction, but I'm starting to see this falsehood in more and more places.
