Why do people who want to deligitimize Zionism bring up the Khazar argument?

The vast majority of ashkenazi jews have no khazar blood only (12.7%) patrilinially show DNA halotypes to central asians. They are decendents of Semites who migrated to Serbia Croatia Greece and Austria some mixed with Greek and Roman converts and then migrated to France and Germany after the fall of the roman empire. And then went to Eastern europe after the crusades drove them out of western Europe. But does this legitimize their claim to the land even if they left 2000 years ago. If they were pure decendents and palestinians were martians would this justify occupying the land?