It wouldn't be under seige, would it - if Israel did not see the need to defend itself from continual attack. Israel withdrew in 2005, Hamas was voted in - and then they immediately began their jihadi war.
The reason that both Israel and Egypt guard their borders - both at sea and on land, is because Hamas and others use the tunnels to smuggle illicit weaponry and other things; and now because Iran also tries to smuggle in weaponry from the sea.
There has never been a Palestinian state - before the mandate it was part of the Ottoman empire. You cannot return to a country that has never existed. The right of return has made refugees of generations of people; including second and third generation people living in America and elsewhere in the West who have citizenship of the countries they were born in.
Palestinians are the only group who have been made refugees in perpetuity, rather than being resettled. 1,1 million jews were expelled from Arab countries in 1948. -and Israel took them in.
Mahmoud abbas has Jordanian citizenship - and yet we are expected to accept that there are now nine million registered refugees purely on the basis of being descendents of people who once lived in that area.
Israel exists. It is a country and an official state. It is productive and creative, and employs many Palestinians - or it did until the Hamas attack. You could not blame Israel for now not permitting this going forward.
The 'Right of Return' is a fanatsy that keeps populations trapped in a cycle of welfare aid and dependency - and it also breeds hatred. This is perpetuated in UNRWA schools. If surrounding arab countries had absorbed the populations in the way that Jordan firts did ( The West Bank was Jordanian territory), there would be no refugees in the Middle East and people could get on with building a healthy and productive economy and being useful citizens.