A Dyson sphere around a black hole

The whole concept of a Dyson sphere is kinda idiotic. Any civilization that is capable to build one, it is probably able to work out fusion energy very efficiently.

There is no point to go and harness energy around a star or a black hole, when you can just produce it locally with a lot less resources/waste and materials. The sun itself is actually very inefficient in producing energy.

There is no need to harness the sun million of km away, when you can recreate it in your home planet. The only way to produce a dyson like of sphere, is to tame an over-heated sun, and reflect away un-needed energy. But there is no point to build one to just harness it.

It makes great sci-fi stories, but that's about it. Scientifically, it just doesn't make sense.

There is no kinda idiotic. There is a somewhat stupid.

A Dyson sphere is foolish because one can simply build a small local fusion reactor instead of using the giant free one nearby?

Imagine a sphere of reflective particles around a star. Planets within would never experience nightfall. Free energy would be everywhere. Sounds useful.

Moreover, such a solar system would be difficult to detect. If it is mobile, and uses a low-signature form of propulsion such as UFOs exhibit, then it would be extremely elusive.

This solves the problem of someone launching stealth asteroids at one's base at relativistic speeds.

Moving a solar system presumably requires tremendous power. Using a star as the fusion reactor presumably helps.