Youare all missing the Elephant in the room - the ACCC.
While the ACCC is slow, dumb and relatively placid, it is not completely stupid.
Thats why Jetstar is going to have to answer questions if it matches, let alone undercuts, Tigers fares.
There is a section of competition law that relates to
predatory pricing
From Wikipedia
Predatory pricing (also known as
Destroyer pricing) is the practice of a firm selling a product at very low price with the intent of driving competitors out of the
market, or create a
barrier to entry into the market for potential new competitors. If the other firms cannot sustain equal or lower prices without losing money, they go out of business. The predatory pricer then has fewer competitors or even a
monopoly, allowing it to raise prices above what the market would otherwise bear.
Predatory pricing is illegal in Australia, and in my opinion, Qantas has engaged in it for a very long time, but not continuously.
From memory, and not being a lawyer, I think it is illegal for a company with a substantial market share, which Qantas undoubtedly has, to price a product at less than its cost of production to the company.
The trouble comes howevr when you attempts to prove it, since I no of no forensic aviation accountants available that would want to blight their employment prospects by helping the ACCC pin this on Qantas.