I would agree with giving Gaza & the west bank back if there was a method of ensuring Israeli security and decreasing palestinian hostility by doing so. However, Gaza & the West bank weren't even Israeli property until 1967. For the first 19 years of Israels existence Egypt & Jordon controlled them. There was no mention of 'liberating' them when arabs controlled those territories.
I disagree with the 1948 part. The Palestinians renounced that deal. Besides, the Israelis have invested many billions in building up Israel, they shouldn't give 1/2 of it to the Palestinians.
Also, what of the 900k Jews who had their land stolen and their money taken when they were kicked out of the Arab states from 1948-2003? Shouldn't Morocco, iraq, Egypt, etc. give them their land and money back?