Ah, there's Galileo, again. A lot of that stuff is mostly myth. If you actually read about what happened instead of the bigoted Enlightment-era pamphlet pulp that's been absorbed by our textbook writers (horrifying to ask how much of that stuff is actually credible), you'll find that, first, he was a promoter of heliocentrism, a view that did not originate with him but one which he embraced following Copernicus and which goes back to at least Aristarchus. Second, at the time, heliocentrism was not better supported than geocentrism or one for which there was extraordinary incentive or pressure to adopt or address, nor was it some idea people (typically supposed to be Church prelates) were somehow afraid of, though FWIW, Copernicus was afraid of academic opinion, not the reaction of the Church (he himself was a member of the clergy and had corresponded with one or two popes, bishops, etc, about his work). The so-called Galileo affair spanned decades during which Galileo insulted and harassed political and Church authorities which, frankly, give the impression of being rather slow to anger. One contention that Galileo (who died a Catholic, btw) had concerned the language in the Bible that spoke of the rising or setting Sun. If heliocentrism is correct, then why is the Bible speaking of the rising and setting Sun? I don't know about you, but that strikes me as a pretty stupid question. To this day, we speak of the rising and setting of the Sun. It's descriptive language, not a scientific description, and the Bible is no scientific textbook. Maybe monomania is to blame for thinking that it is.

W.r.t. Semmelweis, I don't know how this played out, so you'll have to fill me in. I would make an initial distinction, though. The first is that once a theory achieves widespread acceptance, it's not surprising that honest people will be slow to absorb something that they can't account for. It takes time to process evidence. Think how absurd it would be to just throw away something that's made sense up until now. You have to reconcile new observations and do the work of accounting for everything accounted for by the previous theory plus the new thing. Throwing it away just like that leaves you with nothing to work with. The second distinction is that a lot of people build their egos out of knowing something and the feeling of dominance they get from it. "I'm hot shit and superior to you because I know X." Then you get these little cliques and cults of affirmation which adds another barrier because now you face the Lomanesque risk of no longer being liked.The coward cannot bear that possibility so he "defends" his tribe to protect himself. Of course, he isn't really acting for his own good or the good of others, just his own comfort.

But in general, yes, academic fads and prejudices do exist. Try being a conservative at a major university today, especially in a humanities department.