Are terrorists going to be deterred - are terrorists going to be scared if we react violently? No. They love it. That's what they dote on. They dote on violence. They dote on having more reasons to commit more terrorism.
The violence of our time is caused by obedience.
I am not an absolute pacifist, because I can't rule out the possibility that under some, carefully defined circumstances, some degree of violence may be justified, if it is focused directly at a great evil.