Originally posted by Jon Toner:
Is it any surprise in an era where prevailing morality is, "It's only wrong if you get caught?" that you'd have (1) morons bragging how much they love to steal, and (2) reporters giving these idiots a forum?
It is one thing to "work the system". Maximizing your benefits within the confines of a system defined by others is completely acceptable.
Outright theft is another thing entirely. It doesn't matter if the seat is sitting there empty. It means slightly better service to the folks who earned/purchased those FC seats!
Like Boomer, I fly CO, which almost always has full FC. I'd imagine this stunt would be harder to execute there.
Ditto for UA - the rest of the employees sitting there wouldn't recognize the thief. 
Jon, couldn't have said it better myself.
Unfortunately, I saw this happen once on a Continental flight. While waiting for the FC lav, I heard the two FA's discussing the passenger in 4A who was in the seat but not on the manifest.
During the duration of the flight, I watched as the woman ordered drink after drink, until the FA finally cut her off.