Agree, also it is terrible UX if it is not apparent when you can not decide for yourself whether you are the target user. It isn't hard and it saves from these two scenarios:

1. Oh, this isn't for me, glad I found that out quickly - saved me lots of frustration.

2. Yeah, I'm not the target audience for this but I know of another niche where this is useful despite that - I might actually try it out!

It also gives a very bad impression of the company to actively not caring about frustrating users they are not interested in.

Seems I paraphrased the article poorly, here are the actual key points:

1. Never assume you know more about a design than the company that made it.

2. You don’t know the problem that the design is solving.

3. Don’t jump to conclusions until you have data to back it up.

4. You don’t have to be right to be a good designer. You just have to listen when you’re wrong.

5. Always test. Always.

6. There are no UX best practices.

In general I tend to align with you though. Do right by the user, and its probably the right thing for your company too!

If the problem the design solves is the designer's problem but not the user's problem, then it is definitionally a bad user experience.

You could call it a well-executed exploitative design, I suppose, but you can't call good UX when the U has an X that is by their lights bad. And even calling it "good design" only works if one thinks design has absolutely no ethics built in.

As a comparison, you can't really call what Josef Mengele did "good medicine". It doesn't matter how technically skilled he was or how much he accomplished for his employers, because medicine is deeply and explicitly patient-centered. Many designers believe that unethical use of design skills is flat out bad design, no matter how much money it makes.