Couldn't you employ the same "free speech" logic to someone ordering a murder?
Again, it's not the speech that's being criminalized; it's the intent animating it. Think of the link not as a crime in and of itself, but simply as evidence of Brown's effort to assist in the real crime, which was unambiguously illegal. If you follow the case closely, you'll see that's exactly what's being charged.
This doesn't strike me as very productive. Whether sharing a link can be a crime is, of course, exactly the point under debate.
And I don't see how you can dispute that whether sharing a link is a crime depends on what is accomplished, and what is intended, by sharing the link. There is, of course, no law that criminalizes sharing a link per se. But there are plenty of laws that criminalize things you can do by means of sharing a link. Take GP's example. You write up a murder-for-hire ad on your private server and post a link to it on HN. That's solicitation of murder, no less than if you had made the solicitation in person or by mail. You may as well argue that talking to someone, or sending a letter is not a crime.
Again, it's not the speech that's being criminalized; it's the intent animating it. Think of the link not as a crime in and of itself, but simply as evidence of Brown's effort to assist in the real crime, which was unambiguously illegal. If you follow the case closely, you'll see that's exactly what's being charged.