That's my point. You can't simultaneously hold both points of view. They are directly contradictory.
If there is no justification for death threats, there is no justification for death threats.
You keep justifying the behaviour by saying the cartoons shouldn't have been shown.
Why shouldn't the cartoons have been shown?
Because they caused offence?
Is it ok to feel offended?
Yes, of course it is. It happens to people all the time that they feel offended by something that wouldn't concern the next person. Causes of offence are not universal. We have to accept that we can feel offended because not everyone believes in what we do. And that's OK.
But as we've already established it is not ok to issue death threats.
So if there is no justification for death threats what the teacher did is irrelevant, even if it caused offence. Even if he was aware it would cause offence. None of that can ever justify death threats. There is no, 'The teacher shouldn't have offended Muslims by showing the cartoon." There is no, "The school should apologise." That position is logically impossible.
There's an irony that people who are defending the protestors can't grasp what was essentially being taught in that class is the way to tolerance.