<font face="Verdana, Arial, Helvetica, sans-serif" size="2">This is clearly NOT stealing ... </font>
It's not stealing? It's taking something that has a price on it (miles, money or certs) for which you did not pay - that's stealing. We've had other threads about this in the past where on some airlines FAs get out the charge card machine and tell the person to either pay up or move back. In all cases reported here, the person quickly moved back. If you were caught stealing a first or business class seat and you did not move back, I would certainly think the crew could have you arrested for theft (among other things) upon landing.