I would categorize it as 10 percent humor, 60 percent temporary interest in the vague threat implied by the "don't do this... or else" definition and why that context was appropriate when applied to the topic of contradiction, and 30 percent etymological interest, as I have "on pain of death" as the most-associated thought when hearing the phrase (Google agrees, with that as the top suggestion to complete "on pain of"), and was curious as to how the permutation may have originated.

ETA: I disagree with the sentiment that contradiction is a negative, undesirable, or potentially painful event; instead, I view it as an opportunity to update maps, assuming that the contradiction is supported by the weight of the evidence.