We have laws against negligence where if some person fails to take proper precaution to protect the safety of someone else, the negligent person can be found guilty.
This only holds when the person who didn't take proper precautions had some duty to protect that other person's safety.
That is exactly what I mean, should we be responsible for the actions of our brains and arms when, say, building a house so that it is not a firetrap even if the builder will never meet the one who may be triggering the fire with a ill thought that added a bit too much pine wood that triggered sparks and a chain of events?
Should we be responsible for what our brains and mouth does when we state something? Even if the speaker will never meet the person
Then, we have the philosophical question: Can speech influence behaviour?
Of course it can; it's not much of a question. Ask any Internet troll.
That was a rhetorical question by the way. It is not my intent to waste your time and energy to answer those.
If we can agree that one person's speech can influence another person's actions, can we then come to the conclusion that one person's speech can put a third person (or her/his possessions) in danger? If we think that the answer to that question is yes then the natural question to follow up is: Are we allowed to put another person (or her/his possessions) in danger?
Your logic doesn't hold together. The intermediary matters. If I point a gun at a person's head and pull the trigger, I've "influenced" the bullet to kill the person, but I'm the one responsible for the death; neither the gun nor the bullet is capable of judgement and cannot be held to blame.
On the other hand, if I merely say that the world would be a better place with that person dead, I may influence some listener into killing that person. My speech has indirectly caused someone else's death. But this time I'm not culpable; the other person is not an automaton, they have the capacity to make their own decisions, and I am not responsible for them even if they got their bad ideas from me.
Of course there are grey areas; perhaps I have some authority over the second person and perhaps I'm in the habit of giving orders by making offhand remarks like that. In that case I might be culpable, both morally and legally. This decision says the prosecutors have to demonstrate that this is the case.
Yes, it does in fact hold together, it might not seem like so if one ignores how the human cognitive system works, while we would like to have black and white laws and rules that governs our behaviour we can not because our perception and actions in this world are subjective and never black and white.
Our actions do indeed influence others, even when we have no power over them. This is why commercials work. This is why branding works. This is how fanboyism is formed. This is how religion is based, it is all just speech that influences others.
Here is the fact that is the hardest to account for in this discussion, you have problem with it and so do I: It is never a single discrete event that triggers something, it is always a series of events, and if people (as have been shown again, again, and again) does not take responsibility for their actions (like speech, just look how much lies are spewed at all levels of society) then is it not necessary to do something that forces responsibility? I do not claim to know the best response, but I do feel like something has to be done.