I think it's perfectly valid to say "I don't know anything about this area". Would you prefer him to say "I will arbitrarily assume (because I have no informat

I think it's perfectly valid to say "I don't know anything about this area". Would you prefer him to say "I will arbitrarily assume (because I have no information whatsoever) a hypothesis that every person has a unique set of bacteria and see if that is right"? That might actually lead to an experiment that misses what he found: you would probably take similar people. If you hypothesis that people have similar sets of bacteria, you'd want to pick wildly different people. Sometimes we don't even know enough to ask a useful question, but it is still scientific to examine the area with repeatable experiments and see what you find.