It's interesting to draw a parallel between the author's argument that Semmelweis could have achieved more if he had been more respectful and "never antagonized so much of the medical establishment" to similar arguments continuously leveled at Martin Luther King, Jr. and other civil rights leaders. Despite this same argument being dredged up whenever there's a conflict between reform and inertia, history provides few examples of polite, demur, reformers who were careful to never antagonize the establishment.
It's also worth pointing out that the phrase "it's conceivable that" is a fairly cheap rhetorical trick: you can advance any ludicrous argument with no evidence or material support while forcing anyone who disagrees with you to produce proofs that are beyond all reasonable doubt. "It's conceivable that if the Nazis had won WWII, we would have colonies on the Moon by now." "It's conceivable that Yahoo's stock price will increase ten-fold in the next year." "It's conceivable that eating dog shit is the key to human immortality." Sure, it's conceivable but because it's neither plausible nor likely, and because no valid argument can be advanced to support the claim, it's not worth talking about, unless we're writing alternative history fiction. Yet authors often use this or similar phrases to propose arguments that they personally believe but know they cannot defend.