I agree with you— I think it’s one of those “well our tools of analysis only work under an assumption of rationality, so we have to state it as an axiom” things.

Yes.

Its hard to say waht is rational in the generic as it is often situational. Its rational to prepare and save for the future but if no amount of savings can get something substantial. Lets say like a house. A rational mind might not see much of a point to saving for it. Compound this with a future that seems to be rigged, lets say but investments or savings that seem to lose over time. Well what is rational changes.