I don't think this opposition is so absolute, though, between on the one hand wanting there to be a large pool of unpredictably assigned judges, and on the other hand wanting them to be familiar with the relevant law. For instance, given that there exists such a thing as a license to practice law, perhaps juries could consist of randomly selected lawyers, instead of randomly selected people-in-general. If I were more awake right now I could probably start poking holes in that idea, but I do think it at least serves as a counterexample to that dichotomy.