Classic,
I think Juud was refering to "when it gets more serious".
The point is that a lawful direction from the Cabin Crew must be obeyed by passengers, and passengers need to be aware that there can be consequences if they insist on playing hard ball.
Arrest on board, as you say, is not really an option if the passenger is simply refusing to turn off an electronic device... but going back to the gate and offloading, or having authorities scare them on arrival is.
Usually the threat of offload/going back to the gate is enough to make them turn it off!