You could. But ID checks are sometimes done at gates. And if caught, expect to hear on the local news - "next, at 11 - a major gap in Airport Security found". with images of worried mothers saying "i think that's crazy someone could get on the plane with someone else's ticket - I mean, who knows what that guy wanted to do (I don't know, something crazy like get on a plane and off a plane?)

Even though this is a revenue issue, not a security one, and the ticket user is 99 percent not a terrorist. And he would need to get into the sterile area with a BP or gate pass that went through the no-fly list stuff...