it's an internationally recognized right, which everyone except Israel (and by extension the United States) refuses to accept.
And it's not about "destroying Israel" either - although that is really a nice inflammatory right-wing talking point, which I don't understand the worth of repeating here.
http://www.hrw.org/campaigns/israel/return/ * The Universal Declaration of Human Rights (10 December 1948)The right to return has a solid foundation in international law. Article 13(2) of the Universal Declaration of Human Rights (UDHR) states, "Everyone has the right to leave any country, including his own, and to return to his country".
* The International Covenant on Civil and Political RightsThe right to return is most clearly enshrined in the 1966 International Covenant on Civil and Political Rights (ICCPR) under its provisions on the right to freedom of movement (Article 12).
* Convention Relating to the Status of Refugees (28 July 1951)International refugee law and international human rights law mutually reinforce each other on the right to return.
* United Nations General Assembly Resolution 194 (III) of 11 December 194811. Resolves that the refugees wishing to return to their homes and live at peace with their neighbours should be permitted to do so at the earliest practicable date