What is non-niche by your definition?

Building a super yacht means that dozens or hundreds of people work for the benefit of one person. As craftsmen, they could have improved the lives of tens of thousands in their community instead. As engineers, they could have built products serving millions.

Not to mention the natural resources used for one person's benefit.

There's nothing positive about super yachts (and mansions, private jets,...) being built. Don't let the flow of money confuse you.