The problem is, the answers are useful to more than just the original questioner. Sure, the questioner may be doing things vastly wrong - but the people who land on that question's page via search may have legitimate reasons for doing things a certain way.

The silent majority of viewers will benefit from an answer that does both of (1) explaining why the answer is probably not what is wanted, and (2) answering the initial question _as written_ anyway, for future viewers.