Well I never mentioned the Khazar theory, but since you brought it up, the following eminent Jewish academics blow your puerile, "...debunked and laughed at by all historians" comment out of the water. Avraam Yakovlevich Harkavy was the first academic to postulate the Zhazar theory, not Schlomo Sand. Then the theory was developed by, amongst many others:
Joseph Jacobs
Maksymilian Ernest Gumplowicz
Samuel Weissenberg
Maurice Fishberg
Yitzhak Schipper
Samuel Krauss
Abraham N. Poliak
Ben-Zion Dinur
Salo Wittmayer Baron
Arthur Koestler, probably the most famous amongst recent historians.
For every academic that subscribes to the Khazar theory, there is another that disagrees, Stampfer is just the latest who "disagrees"; currently it's still not proven, either way and irrelevant to the fact that the Palestinian Fellahin, or whatever you want to call them, were always there, whatever religion they chose to follow or not.
As an aside, the Khazar theory has often been hijacked for political agendas, especially with Christian far-right white supremacist groups in the USA:
"The formative period of Christian Identity could roughly be said to be the three decades between 1940 and 1970. Through missionaries like Wesley Swift, Bertrand Comparet and William Potter Gale, it took on a white racialist, anti-Semitic, anti-Communist and a far-right conservative political outlook.
Combined with the teachings of early disciples Richard G. Butler, Colonel Jack Mohr and James K. Warner, a distinct racist theology was gradually formed. Whites were said to be the Adamic people, created in His likeness. A notion of a pre-earthly existence is found in an important substratum, teaching that whites either had a spiritual or extraterrestrial pre-existence. Blacks were either pre-Adamic soulless creatures or represented fallen, evil spirits, but they were not the chief target of fear and hatred.
This position was reserved for Jews. The latent anti-Semitism found in British-Israelism rose to prominence. Jews were, at best, reduced to mongrelized imposters, not infrequently identified with Eurasian Khazars without any legitimate claim to a closeness with God, and at worst denounced as the offspring of Satan.'---Religion and the Racist Far-Right.