Personally, I think it's wrong to advocate murdering anyone. I also think unless there is a direct threat made against one or more persons, freedom of speech plays in. Saying you're going to murder the family at a specific address is a specific threat; explaining how to kill officers, while completely immoral, is not a specific threat, it's an explanation.
Hate crimes are another, relatedproblem--they supposedly punish a person for what they think. Parole is another problem--it's based on how people who write letters to the parole board feel. People shouldn't be punished for what they think or feel, but actual criminal acts they commit, IF they commit them.
That shouldn't weaken our legal system--a bad guy who says to an officer, "I'd really like to hit you right now," but stands there motionless, has obviously expressed an opinion, and he has the same right to do so as the officer has in responding, "I hope they convict you of the drug-related murders we arrested you for and you get the chair." If the statement from the bad guy is, "I'm going to kill your family as soon as I get out on bail," that's a different story, and the court should step in.