It never ceases to amaze me that there are so many pilots and flight crew out there who could (and perhaps have!) successfully manage an emergency in-flight, but apparently can't negotiate or de-escalate a difficult situation with a fellow human being. It indicates a concerning lack of empathy. As an aside - CASA seems to be obsessed with preventing autistic people getting a medical certificate, yet I've met many pilots who I'm nearly certain were somewhere on the spectrum judging by their inability to empathise and read social cues.
If you think that someone being tasered is an appropriate way to resolve a dispute over where someone is seated you should seek help. Obviously it's the AFP that have done the tasering, but the fact that the crew were unable to negotiate with a man that was reportedly not being aggressive or violent says a lot about how little emphasis is placed on customer service training and dispute resolution at Jetstar.
I wonder if the Captain or FO went down to have a reasonable discussion with him and to listen to his concerns? Not mentioned in the article.