Thanks, that helps update my knowledge of the current standards. I certainly agree that what you say is reasonable, however I do not think that a potential for a slippery slope effect can be eliminated through carefully formulated test or doctrines (merely substantially reduced). For example, it is conceivable that in emergencies the fact that we now accept some restrictions on free speech will make it much easier to accept further restrictions and thus make unreasonable restriction more likely.

Whether that is a reasonable compromise depends on the actual danger of "pure speech" causing negative consequences, on alternative ways of mitigating them, and on the actual degree of the slipperiness of the slope. Personally, based on my current knowledge, I would prefer to pursue various alternatives before resorting to criminal legal action, however that's dependent on actual facts and has little to do with the main topic being discussed.