When that single plane incident didn't do the damage they had hoped it would, terrorists would have to find something more spectacular that could not be denied or discounted as accidental. And they did.
I don't think that was just an isolated incident by a distraught man- IMHO it was a calculated act by a terrorist who probably has other associates we should be looking at but haven't, at least not publicly.
Like it or not, though, it is better for us economically to pretend everything is just an accident that can be fixed if we just solve some technical problem with the equipment. The stocks people get the willies if only fix for the problem is war.