People may shrug the story off as an outlier, but the fact remains that if consent is the only barometer of legality and moral licitness, nothing is off the table. A nod of the head, a signature at the bottom of a notarized contract, and actions like cannibalism—which is correctly regarded as appalling—would be permissible.
Consent as the sole test of moral correctness has a deeper problem: it violates the principle of non-contradiction, which declares that a thing cannot both be and not be at the same time, i.e., stealing $20 from your parents cannot be good and bad at the same time. The ideology of consent breaks the principle. For example, if Fred and Ned decide that cannibalism is good and agree to engage in it, cannibalism is then considered good for them, but if Jim and Tim decide that cannibalism is wrong and do not agree to engage in it, then it remains wrong for them.
This raises a whole host of questions: Can a legal system exist where the propriety of actions constantly shifts depending on the whims of individuals, whims that can change from day to day? Can we even engage in reality if we disregard the principle of non-contradiction?