Are extreme measures sometimes justified when combating terrorism?

Good question, nice perspective. The answer is no, brutal tactics from either side can never be justified. Retaliation begats retaliation. Vengence breeds vengence. Terrorism propagates terrorism. One man's terrorist is another man's freedom-fighter. Excessive force only results in the marginalization of the minority. This causes civil unrest, hence more violence. It solves nothing, The only purpose it does serve is to provide the 'extremists' / army with yet another martyr.