Ahh right, because there was no blockade or violence prior to the Palestinian people electing Hamas as its government. Oh, wait a moment, there has been violence and blockades in Gaza for 50+ years...
Hamas is just the current excuse for the Israeli pressure, not the underlying reason. But its an excuse everyone buys and that's enough.
Before the current rash of violence on both sides, Israel was more than happy to deal with the PLO, whom it handed over "power" in Gaza to in 1994 despite the PLO being responsible for as much anti-Israeli violence as Hamas ever has.
And since the current rash of violence on both sides, Israel is still more than happy to deal with Fatah, which is the continuation of the PLO, and has been merrily firing rockets into Israel alongside Hamas and other groups for the past decade, but we never hear about that...
So what's so bad about Hamas? Oh, its in power and thus can be used as a whipping boy to justify the continued pressure on Gaza and the West Bank.