I think you misunderstood bk613’s (correct) point.
(S)he is saying that it’s silly to assume or even be chosheish for a correlation between autism and vaccines when there is no proof. The analogy to learning gemara has nothing to do with it being a mitzvah, just that it would be silly to think it causes heart attacks just because there’s no evidence to the contrary. If you don’t like that analogy, we can use many more. For example, I think we should stop posting on the CR because it has never been definitively proven that posting on the CR doesn’t cause severe hair loss. (Although, anecdotal evidence has shown that it can cause people to lose their heads…)