All jokes aside, I think this makes a whole lot of sense. CEO Chris Langton summed it up perfectly that you're not paying for the seat, you're paying for the weight.
I don't think there's a difference on whether you're carrying-on that extra 10 pounds in your suitcase or in your gut. Ten pounds is ten pounds.
"Your weight plus your baggage items is what you pay for. Simple."
I wonder when Caribbean Airlines is going to start making Trinis put down those doubles and that bottle of rum before they fly?