Perhaps you are unfamiliar with this idiom. "Mental gymnastics" can be motivated by emotions, but they don't have to be. It isn't motivation that makes any particular mental activity gymnastic, but rather it is incoherence. The commissioner writes as if [0] doesn't exist, even though he probably had it open in another window on his screen while writing the dissent. Ideology and avarice were probably more salient motivators than emotion.
[0] https://www.law.cornell.edu/cfr/text/47/15.5#b