But to be fair to the person you’re responding to, you still haven’t answered his actual question - who gets to decide?
The example you gave is only “obvious” because the majority think so. However we’re increasingly living in an environment where people are “fleeing the centre”. People have abandoned authority, and are increasingly abandoning science, even to the point of doubting or reinterpreting their own lived experience.
The key to “common sense” is “common”. When very little is held in common, where do you find common sense?
This is precisely why, in my view, the single greatest danger to mankind is - a “meta-danger” perhaps - is the explosion in deliberate attempts (irrespective of motive - lulz, commercial profit, political influence or psychological warfare) to misinform, sow discord, and erode trust. It is an absolute scourge and is already starting to bite us in the collective arse, by limiting our ability to act collectively for objective common good.
I have no idea at all how we fight this threat.
EDITED: SP. collect > collectively