With the exception of a very small minority with rare medical conditions and pumped-up athletes, people are considered obese simply because of a self-imposed habit of consuming more energy than they use. It's not the fault of the food industry, government or society. The hand that selects and scoops up copious amounts of food while laying on the couch belongs to the person that is individually responsible for their own ballooning body shape...
So should an oversized traveller pay more than others on an airline? Absolutely! Basic physics dictates that in order for a plane to get off the ground, a major consideration is the weight onboard, not the number of passengers.
If you send off a courier package to another destination, doesn't make sense that you'll be charged according the weight and bulk of the item? So does it make sense to charge airline passengers per-kilo as well?
No doubt other airlines will be watching Samoa Air's newly imposed per-kilo fare system with interest.
Good on the airline for trying out a world-first fare system as a business solution to manage the weight of its "cargo". Predictably, the new fare regime has been widely reported in the media as targeting and discriminating against poor, blameless fatties. Samoa Air have responded with a smokescreen of social responsibility by claiming that they are trying to promote healthy living. Hilarious!
So will other airlines follow? Probably not - In the travel industry that depends upon online sales, it's easier and less threatening to treat all passengers as a one-size-fits-all commodity.
It's likely that airlines will continue to assume an average weight for its passengers and police weight with overzealous baggage fees;-)
