Where are you getting this from? A 20 year old Gazan would be old enough to remember the day Israel withdrew from Gaza, both its military presence and settlers. A 20 year old Gazan would also remember that that shortly thereafter, when Palestinian businessmen were talking about converting former settlements into resorts and all the money they would make from tourism, Hamas took over. A 20 year old Gazan would remember life before the blockade.
Take a minute to think about that. Israel left Gaza completely, and then Hamas took over. Are you saying that turning over Gaza to Palestinians is the sort of restrictive measure that gives rise to terrorist groups?
You are absolutely wrong about Israel holding all the cards. The blockade of Gaza is a joint effort between Israel and Egypt. The Palestinian Authority in the West Bank refuses to pay for electricity in Gaza. Hamas has diverted aid shipments to its own military infrastructure, preventing Gazans from repairing their buildings, and Hamas has previously insisted that shipments of fuel enter through the border crossing with Egypt because they do not want to accept any help from "Zionists." So how does Israel hold "all the cards?" In reality the cards are held by Israel, Egypt, the PA, and Hamas itself.
Meanwhile, over in the West Bank, Palestinians have plenty of legitimate complaints yet the PA manages to engage in joint security, law enforcement, and economic efforts with Israel. Sure, things could be better for the Palestinians in the West Bank, but that is exactly the goal of the peace process and all those joint efforts.
You seem to be confused about cause and effect. The situation in Gaza today is not the reason Hamas took power; Hamas is the reason for the conditions in Gaza. Hamas started a civil war among Palestinians, and as a result the PA refuses to pay the bills for Gaza, leaving them with sporadic and unreliable electricity. Hamas kept smuggling rockets into Gaza, then firing those rockets at Israeli cities, resulting in the Israeli blockade. Hamas kept smuggling rockets into Gaza through Egypt, arming Egyptian rebels, and using Sinai as a staging area to fire rockets at Israel, resulting in Egypt joining the blockade. Hamas spread its military assets across densely populated civilian areas, resulting in far higher civilian casualties and widespread damage to civilian buildings when the IDF responds to the rocket fire. Hamas diverted aid shipments of construction supplies to its tunnel network, preventing Gazans from rebuilding their damaged buildings during the ceasefire. What kind of mental gymnastics do you have to perform to conclude that Hamas is merely a symptom of some other problem?