We are a commune of inquiring, skeptical, politically centrist, capitalist, anglophile, traditionalist New England Yankee humans, humanoids, and animals with many interests beyond and above politics. Each of us has had a high-school education (or GED), but all had ADD so didn't pay attention very well, especially the dogs. Each one of us does "try my best to be just like I am," and none of us enjoys working for others, including for Maggie, from whom we receive neither a nickel nor a dime. Freedom from nags, cranks, government, do-gooders, control-freaks and idiots is all that we ask for.
Posture is complicated, because it involves habit, training, psychological attitude, and muscle strength. Further, good posture makes you more presentable and makes you look more confident even if you do not feel that way.
Medically, good posture helps prevent back problems.
Computer monitors, age, shame and shyness, muscle atrophy, and general slovenliness are the enemies of good posture: shoulders back, head up, no slouch, belly tucked in, etc. Look good, not proudful but self-respecting.
I sit at a desk all day. I do not have good posture. I also rarely have back pain. I have one shoulder that overreaches during the day with keyboard/mouse, but my back? Minor problems that can be corrected with a relaxing sit on the couch! (I'm not kidding)
I get back problems when I walk slowly for long periods on concrete, such as strolling through Costco or Walmart. Of if I stand too long in a line without moving.
So, clearly, there is another piece to the back pain story just based on my own experience.
And just to make it clear: I don't do yoga, core exercises, or sit in a pricey desk chair.