Operation First Rain is under way. A missile blew up during a Hamas rally, so they blamed Israel and shot 35 missiles into the Negev. So Israel decided to do the smartest thing: retaliate hard. The primary security-oriented supposition that Disengagement was based on was that the IDF would retaliate hard for any cross border violence because the Palestinians would be violating an international border.
No one seriously thought the border would remain inviolate. Supporters of Disengagement thought Hamas would be smart enough to wait a little bit before attacking. Israel is basking in solid international support right now; its standing around the world is probably its highest since Oslo in 1993. Attacking now is just dumb, but Hamas did not want to look incompetent so they had no choice but to attack Israel for its "crime" against Palestinian civilians. Well, it's time to reap what they sowed.