Comment by praestigiare

The phrase does not mean that you can pick any single effect of a system and claim that is its purpose, as your linked article does in its examples. (Ironically, a form of reducto as absurdum.) It is a heuristic, a pattern of thought to attempt to overcome the bias towards judging systems based on the intentions behind them instead of the outcomes they produce. The point is that when you choose a course of action, you are implicitly choosing its negative effects as well, and the choice should be judged on all its effects. You are making a cost / benefit analysis, and if that is not explicit, it can easily be wrong.