If we're talking about backs, then (given the very limited amount of literal back-breaking work carrying loads that are far too heavy for us, at least in the de

If we're talking about backs, then (given the very limited amount of literal back-breaking work carrying loads that are far too heavy for us, at least in the developed world) the main damage to our backs is caused by excessive sitting (for which our backs are poorly designed) - so if you're really going to use "damage to our backs" as an argumant with respect to cars vs "biological locomotion", this is an argument for more "biological locomotion" not less.