Earlier quoted context omitted.
“The purpose of a system is what it does.”
Sure, if you completely ignore the meaning of "purpose". What an asinine sentiment.
Reality doesn't care what you're hoping to achieve with a system, the outcome won't change based on thoughts and ideas. Since reality tends to be fairly complicated, we usually won't design perfect systems on the first try - instead we have to analyze the outcome, and make changes to nudge the results into the direction we want.
But what if we don't do that? What if we stick with the initial approach even after we measure that the outcome doesn't align with our initial intentions, maybe even introduces unwanted side effects?
It would be fair to say "well, we tried our best" if nobody was able to have hidden intentions, but that's not the world we live in. People can be very, very happy about our systems not aligning with our intentions & introducing unwanted side effects because this misalignment advantages them in some way. These people can then block changes to the system to keep these advantages alive.
I believe a small fraction of decision makers is enough to keep most systems fixed in such a misaligned state, and we'd never do anything about it if we followed your logic.