The security worry isn't extra laborers driving down wages, it's terrorists coming across the border and blowing up Mardi Gras (secondarily, serial rapists or murderers or what have you coming here to ply their trade). Prevention of entry is the only defense there, because presumably those bad actors aren't here for the long haul, economic gain, etc.
I haven't seen a budget breakdown so I can't speak to how defensible the budget is, just that it seems clear that removal metrics don't tell a useful story on their own.