They have to erase the enormity of the crime from history altogether. Then it becomes easier to justify Israel's destruction because the Jews were thieves who stole the land from the Palestinians rather than the victims of a genocidal initiative against their race. Its hard to justify atrocities against a victim but against a brigand all manner of reprisals can be defended. So there is a vested interest in Holocaust denial. Its a veritage cottage industry among neo-Nazi and Islamofascist websites around the Internet and the bottom line they spout is the Jews lied. Discrediting the victim is the first step in making anti-Semitism fashionable again.
(The Palestinian terrorist regime is the crisis and Israel's fist is the answer.)