They object to Israel officially being designated a Jewish state - a state for Jews primarily. They object to this because they believe it will entrench already pervasive discrimination against Arab citizens of Israel and because they believe it obviates the refugee right of return. Abbas' statements show he is willing to compromise on the right of return, but he simply cannot concede it prior to negotiations. He must get something tangible in return for the refugees.
Turkish police fire tear gas as clashes break out during May Day protest in Istanbul (Reuters)