it is because of their disrespect of a sacred month that you are also allowed to retaliate against them in a sacred month. if any one transgresses against you you also may retaliate against them to an equal extent. have fear of god and know that he supports the pious.
الشهر الحرام بالشهر الحرام والحرمات قصاص فمن اعتدى عليكم فاعتدوا عليه بمثل ما اعتدى عليكم واتقوا الله واعلموا أن الله مع المتقين