Not hiring kids because they’ve used drugs is ridiculous. It’s on AFTER they join that it becomes the military’s business. So yeah, I would say rejecting candidates because they have the remnants of that joint they smoked with their essay last week is a bad idea.
Weed is a problem because as states legalize it, use becomes normalized and Soldiers rationalize that if it's legal I should be able to use it. Even though it's against military policy.
Sadly we are not kicking out repeat offenders due to serious manpower shortages and low enlistment rates even with 20G enlistment bonuses for some positions.