Since 1591 when the flush toilet was invented and common by the 60s and 70s, we have been BM-ing in a position non conducive to getting the job done in a way our bodies were intended.
You see, our bodies have something called an anorectal angle, a bend in the pipes between where waste is held and where it comes out. This bend is at 90 degrees when we stand, and about straightened out when we squat. Sitting down while inviting movement is working against the way our bodies work, increasing abdominal pressure that cause the veins in our anuses to swell, painfully. When those veins stay swollen, they may bleed. Welcome to Hemorrhoid City.
If you don’t believe it, try it yourself as Slate’s Daniel Lametti did. He said he gained an hour of time each week, saved some effort along the way, and his knees stopped hurting after about the third day.