Actually, I don't quite think that the dude punched the porno-er because he was watching it there, but probably because Wright needed to use the computer, realized that this creep was just using the PC for porno surfing, there were probably some words exchanged over it (as in, why are you wasting time looking at stuff you shouldn't be looking at on a library computer anyways?). I doubt that a normal and healthy 25 year old would seriously punch anyone over watching porno, publicly or privately - I know I wouldn't, but if I had to use the computer and this guy was doing the same, well, I wouldn't have punched him but I would have reported him on the spot.