I don't agree with that... the fact that you can be punished for something is by definition an attempt to stifle the behavior that you are punishing. In your example, calling someone a bad name on the street is not something that can be prevented by law, so we add a punishment after the fact to try to prevent you from doing it in the first place.
A better (and more arguable) example would be if someone distributed something that could be used to cause damages or used illegally (say, brass knuckles). In some places they are illegal to own and some places illegal to distribute, some places they aren't. In either case, the only use for them that I am aware of is destructive, unless you count the 'paperweight' argument that is used to circumvent some of these laws. Now, Joe Distributor sells a pair of brass knuckles to Guido Gang Enforcer, who promptly beats someone within an inch of his life. Either they are illegal to distribute, in which case the distributor may be liable for the actions of the purchasor, or they are legal to distribute, in which case the distributor is NOT liable for the actions of the purchasor.
In the DeCSS situation, the court has said that the distribution of DeCSS Source Code is acceptable and protected by the 1st Amendment, therefore it is legal. Therefore the MPAA or anyone else cannot seek damages from the distributor of the DeCSS Source Code.
Note that nothing prevents them from going after the person who compiles and uses the DeCSS software however, as this person is in violation of the DMCA. (All arguments as to the usefulness of DeCSS aside... :)