The truth, as with most historical decisions involving both institutional rule-enforcement and the specific vulnerabilities of the people those rules fall hardest on, is somewhat more complex.

The amateurism rule was real, and it was genuinely applied.

The Olympic Games of 1912 operated under a clear prohibition on athletes who had received payment for athletic performance.

The rule was not invented for Thorpe.

The question of whether it was applied selectively — whether other athletes who had done similar things were protected by the fiction of assumed names while Thorpe, who had played under his own name, was exposed — is a legitimate one.

What is documented is that the practice of college athletes playing summer baseball for pay under false names was widespread, well known, and tolerated.