I have to wonder why people believe that 1967 lines represent some sort of set in stone boundary with regard to a Palestinian Arab state. The one thing that people (especially those who support the Palestinian Arabs) conveniently dismiss is the basic fact that there has never been a Palestinian Arab state. Thus, any borders of a Palestinian Arab state would have to be artificial and arbitrary, so to insist that Israel retreat to the lines pre-6 Day War is nonsense. Those lines had Jordan and Egypt as neighboring countries.
The 1967 lines really are invoked due to UN Resolution 242, and 242 was never intended to be a declaration of the borders of a Palestinian Arab state. The territories referred to in 242 were subject to dispute between Jordan, Egypt and Syria and I think that any honest historian will admit that 242 was intended to ensure that whatever peace Israel made with Jordan, Egypt and Syria, the borders of Israel that existed prior to the 6 Day War would be expanded in some regard. The security of Israel was paramount, trumping the need to hew to some artificial and fluctuating line on a map. The fact that Jordan was considered to be the Palestinian Arab homeland (with Israel being the Jewish homeland) can not be ignored either, as the likely outcome of 242 was expected by many to be the absorption of the Palestinian Arab population in the disputed territories by Jordan, which had and would continue to have a Palestinian Arab majority.
I can’t say what the starting point of negotiations should be, but people should have one thing clearly in mind when discussing lines and borders: unless Jordan and Egypt step up and decide that they will take control of the West Bank and Gaza and absorb the Palestinian Arab populations therein, with full rights as citizens of the respective countries, I don’t think that the 1967 borders should be the starting point for any negotiations that lead to the creation of a new Palestinian Arab state (to me, a non-starter, as Jordan should be recognized as “Palestine” for purposes of the Arab population, even though Jordan made the Palestinian Arabs holding Jordanian citizenship stateless by unilaterally revoking citizenship in recent years.