I think your first point touches on an important question when forming laws. Is it more important to catch the guilty or to avoid punishing the innocent? The settings you apply to this question is quite important, I would argue a balance towards the second option.
Whilst I agree with the sentiment of non-violence, I'm not sure a law like that would not have unintended side effects. First and most important of all, what and who defines a terrorist organisation?
A terrorist group is an organization that uses or promote the use of violence to achieve their aims. A court should create a list of terrorist groups. Most of these groups publicly announce their intentions, so they can be identified easily.