I think this is the only option that ticks all the boxes for the solution I've been trying to find in my head.
Those are the words that were used to accuse Chelsea Clinton of being responsible for the attack - which means according to those who confronted Chelsea Clinton she would meet the standard you have just set.
Do you see the problem?
Violence, other than in direct physical self defense, should be the exclusive domain of the state.
This should be obvious but how does your law work in a situation where, in fact, there is a war and there are people coming to kill us. Or are you naively believing that we live in some sort of utopian post-conflict era, in which self defence against armed groups will never be necessary?
Self defense is legally defined. It's not about a general fear of future outcomes. It's about preventing immediate physical harm. If you're urgently telling people to defend themselves from someone not even in the room, and is actually just a description of a group of people, then that's not self defense in any meaningful way. That's also incitement of violence.
This isn't a theoretical concern. Winston Churchill is an example of a politician who was warning of the dangers of Nazi Germany much earlier than other people were, he was nearly alone in the beginning at a time when other politicians were trying to make peace with Hitler or were openly unconcerned. Your proposal could easily have criminalised Churchill at the time when Britain needed him most.
However, I think there is a distinction between war as a political platform, and incitement of violence. Even when Churchill campaigned for war, he campaigned for the United Kingdom to wage war. He was calling for something that is legal.
The people who inspire the terrorists are not just campaigning for lawful war. They are inciting the masses to commit violence against civilians.
We should be able to differentiate Churchill and Bin Laden.
When it comes down to it, there will always be a situation in which a law makes the right thing illegal. Drunk driving a dying person to the hospital in an emergency is illegal but it's not always wrong. I think laws should aim to maximize benefit and minimize harm rather than stay ideologically pure.
In that light I think in this day and age, it's much more important to disable the ISISs, the KKKs, and other inciters, than it is to enable the Churchills. It's a value judgment here, but how many Churchills are we expecting in the next 100 years? Because terrorists are here right now.