> The idea that indoors needs to be between 72° (F) and 75° at all times is unsustainable.
The WHO recommends a general minimum household temperature of 64°F for all populations for health reasons, with a higher minimum for sensitive groups including children and the elderly; maximums are more regionally variant because acclimitization (which takes years) plays more of a factor in high-heat health risks, but even in extreme regions seems to top out at about 90°F for the general population.
Lots of the US spends lots of time significantly out of at least one end of that range (and, especially given that the top gets lower in colder regions, lots of the US spends lots of time significantly out on both ends of the scale.)
> The other problem is that if you do decide to insulate the house, then you may end up needing to use A/C because the house can no longer be wind-cooled to an acceptable temperature
If you have a house that is insulated well and also lacks doors and windows that can be opened, sure.
But... that presents other problems, too.
The idea that indoors needs to be between 72° (F) and 75° at all times is unsustainable.
The other problem is that if you do decide to insulate the house, then you may end up needing to use A/C because the house can no longer be wind-cooled to an acceptable temperature, and you will need to update the heating system as traditional methods of heating (fireplace, stove, simple furnaces) depend on external air circulation.