whether a majority prefer a default of "All Forums" or of "The Forum I'm in Now."
If we are voting, I'm firmly with Dr. A ...
Let's walk through a couple of examples. Suppose you are looking for the point where Buzsaw already learned something about cosmology that seems to have slipped his mind again. You might logically assume that all this would be happening in Big Bang Cosmology. But noooo, you are in a Flud thread and it happened in Bible Study.
Or again, suppose you are looking for an awesome summary Modulous once gave of "bubble evolution". Yes, this very likely is in Abiogenesis somewhere, but you aren't, you are In The News trying to slap off trolls.
Numerous such cases outweigh any normal logic. Default should be "All Forums".