How simple do you want to go? I happen to like having a house to live in,ac in the summer,heat in the winter,I like my refrigerator/freezer, also not to mention indoor plumbing.
A well sealed and insulated house needs little cooling or heating, and of course we don't need to be cooking ourselves alive inside in the winter while reaching for our sweaters in our Arctic AC in the summer.
Europeans (and most others) generally have tiny refrigerator/freezers if any. They stop at conveniently located markets and street stands to get fresh fruits and veggies, so they don't have to keep them frozen.
Plumbing, once installed, is not a major energy user, but lots of simple conservation measures can cut way back on the amount we use.
How far down should we go tin one room shacks with a dirt floor?
LOL. I'm surprised you didn't drag out the old cliche about "we might as well be living in caves."
Really, Americans always think that any slight adjustment to their obscenely wasteful ways means going straight to third world slums or worse. We are really a pathetic lot compared to our pioneer forefolks (not idealizing them, mind you, just saying that they would be shaking their heads at our pampered perspectives.)