I have yet to see a modern house where I live built without insulation. Yet people still have to heat their houses with furnaces in the winter -- they can't just use the radiant heat from their bodies. Insulation must not work I guess.
I would say that the reason you "guess" is that you've never lived in a house without insulation?
I grew up in one. My folks built a new home when I was 16, complete with insulation, central air and heating, strategically placed windows____the whole nine.
I can truthfully attest to you that insulation "works" big time. May not eliminate all 'troubled climates', but mitigates enough of the effects to make it worth the expense and effort.
It absolutely is miserable here in the South without some form of it.
(By the way, I 'get' why you posted what you did, I just put in my 2 cents worth to see if I can drive the discussions in a different direction. It's really for me, so I can fight back the incredible urge to not talk about the ABSOLUTE CRIMINAL nonsense that took place in D.C. today. Especially since the 'fake media' is talking about it 24/7).
Ooops, I did it again!