Muslim Women Foil Airport Security

This YouTube video is making the rounds. Note the scary music:


The women apparently managed to get on the plane without the gate agent checking to verify their identity. The gate agent is an airline employee, who is required (apparently by federal law) to check the identity of everyone just before they board the plane.
To me, the at-the-gate ID check has always been the most ridiculous part of airline security. To get to the gate, you must pass through the security checkpoint, which is staffed by federal employees from CATSA. During this security check, the CATSA employee must verify your identity using photo ID (note: if they got through the security check without showing their faces, this is obviously a massive breach of security). However, for some reason, after having confirmed your ID at security, the federal government thinks that you need to re-confirm your identity at the gate.
I am having a very difficult time imagining a terrorist scenario which the gate check would prevent. Maybe two terrorists book flights for different planes, get through security, then decide to switch tickets so that they can... do something terrorist-y.