At the beginning of his presidency, Obama made impression he will pressure Israel. He also insisted on Israel stopping construction in Judea, Samaria and even Jerusalem and he referred to 1967 armistice lines. As the result, Pals imagined they could raise their demands and quit negotiations. If UN voted for recognition of PA along 1949 armistice line (falsely referred to as pre-67 "borders"), Pals will never agree on anything else and it would end of any possibility of peace, because Israel will not surrender Jerusalem and will return to ghetto 1967 demarcation line.
Judge orders Jerusalem Gay Pride attacker to undergo psychiatric evaluation (Haaretz)
from the article: Obama: UN resolutions won't bring Israel-Palestinian peace