Information markets have become more efficient over time, and this has asymmetrically improved elite common sense relative to the views of outstanding individuals.

Even if Hume's views were minority opinions, they may not have been flat out rejected by his peers (although they may have been). So the prior against his views being right coming from other people thinking other things may not be that strong.

Even if Hume wouldn't have been justified in believing that the conjunction of all of his views is probably right, he could still have been justified in believing that each individual one is right with high probability.

I think that it's sometimes possible to develop high (~95+%) confidence in views that run counter to elite conventional wisdom. This can sometimes be accomplished by investigating the relevant issues in sufficient detail and by using model combination, as long as one is sufficiently careful about checking that the models that one is using aren't very dependent.

In the particular case of MWI, I doubt that Eliezer has arrived at his view via thorough investigation and by combining many independent models. In a response to Eliezer I highlighted a paper which gives a lot of references to papers criticizing MWI. As I wrote in my comment, I don't think that it's possible to have high confidence in MWI without reading and contemplating these criticisms.