Why do you consider that "Price-fixing that is not done via consolidation is ultimately unstable from game theory point of view." + "there is a very strong ince

Why do you consider that "Price-fixing that is not done via consolidation is ultimately unstable from game theory point of view." + "there is a very strong incentive to defect" would imply that this is not price fixing? Quoting FTC, price fixing is an agreement (written, verbal, or inferred from conduct) among competitors to raise, lower, maintain, or stabilize prices or price levels; Generally, the antitrust laws require that each company establish prices and other competitive terms on its own, without agreeing with a competitor. It doesn't matter if we're in a monopoly situation, it doesn't matter if the agreement is effective or if many participants defect - if some participants agree to coordinate prices, that is prohibited and punishable.