The issue of frame damage is certainly real. But there are other factors.

Which is worse: having a post that is, say 1-2 inches longer than standard spec, or a bike at standard spec ridden by someone who weighs 220 pounds, or ridden by someone who hits a lot of large bumps/holes and does not use the legs as shock absorbers?

I leave it to someone else to work out the precise math, but using a bike only on paved surfaces (as I do), avoiding bumps as much as possible (which I do), standing on the pedals to remove weight from the seat if a bump is encountered (which I do), and being of a reasonable body weight (which I am) results in less stress on the post and the bike than someone who uses a normal post at normal height and does none of the above.