This is a pretty odd remark. The effect of living with one kidney isn't some sort of unknown thing we need to reason about from first principles, we know pretty well what life is like for kidney donors. And I don't know about 'really have to', but it doesn't seem like 'saving someone's life' is a trivial or stupid reason.

Evolution doesn't imply a cause to every attribute. Totally plausible that having one kidney is advantageous, our bodies have general bilateral symmetry of organs, there is no strong selection pressure against having that symmetry result in two kidneys, hence we have two. Most of your DNA is "non-functional". Evolution does not have a plan.

> Evolution has ... for presumably good reasons

That's not how evolution works either in theory or in practice

> Evolution has equipped us with two kidneys for presumably good reasons

As the article pointed out, on average you live a totally fine life with only 1 kidney, so clearly no.

Like, that same argument would be "evolution gave us poor eyesight, so glasses must be bad. Why else would evolution make so many people's vision fail? Blurry eyesight must have an evolutionary advantage", or "evolution made some people white for a reason, don't use sunscreen, skin-cancer research says to sunscreen up, but we shouldn't second-guess evolution and play gods".

Evolution is random mutations with a very course-grained utility function. Rejecting evidence in favor of it gives you nothing but nonsense. And fad diets, but mostly nonsense.

evolution also programmed us to yawn, yet doctors can't figure out what purpose or benefit it has