First off it's not a question of "viewing" it as stealing. It is stealing. Airlines are not selling seats, they are selling transportation with different levels of service and comfort that cost different prices. Take that which you did not pay for and you are stealing. If moving into first is not stealing, then neither is simply walking on the plane into coach without having paid.

The sporting event is the same as are concerts and plays. If I pay for $10 standing room only at the back of the theater and run up and take the $400 box seats, I'm stealing. Most places I go to watch games, concerts and theater productions do seem to have paid staff making sure this doesn't happen though.

On the flip side, I have been to empty theaters and stadiums where the staff has invited people to come closer for the benefit of the players and actors, I presume. This would be the equivalent of an operational upgrade, which would not be any sort of theft.