Originally, the "siege" policy was motivated as the means to make the Gaza population unhappy with Hamas rule and help them overthrow it. It didn't work, and actually should not have been expected to work because historically, Arab masses do not overthrow rulers, Arab militaries do that, but in Gaza Hamas IS the military. The policy failed to achieve its goal, but was continued nevertheless under changing explanations (today it is the Shalit excuse). How much damage can a pointless, visibly failed policy cause? Consider just one example: Operation Cast Lead (late 2008) was caused by the pointless "siege" policy. Hamas offered to continue the then prevailing cease fire provided that Israel lifts the siege. Israel refused. Result: Abbas had to stop peace negotiations with Israel. Olmert said he was very close to a deal with the PA, but then Cast Lead "happened". No, idiot, it didn't just happen, Olmert preferred the "siege" over a peace deal. Such an incredible choice should go into the history books!
Preliminary report: Palestinian stabs man near Damascus Gate, Jerusalem (Haaretz)