If the goal were security, Israel would have built the fence a few km inside its borders. It could then be a mile high, patrolled on both sides by the IDF, mined with nuclear weapons, utterly impenetrable. Perfect security.
The problem would be that it would not take valuable Palestinian land and resources (including control of water), drive out the population, and lay the basis for still further expansion as Palestinians flee from the dungeons that are left, like the town of Qalqilya. So to interpret as a land grab seems appropriate.