Earth orbits, low orbits above all, are a finite resource, and suffer pollution as every environment, with all this kind of satellites growing in number to millions, things can go badly: https://en.wikipedia.org/wiki/Kessler_syndrome

Apart tecnical and scientific reasons (no need to use thousand or million of sats), apart big speculations (suspect is the main reason), many problems can be resolved in others ways.

putting mirrors in orbit to have (little) more light is like buiding city underwater to have more cool. ops this last will be way less stupid in the future... To downvote a different opinion without arguing is same kind of attitude: stay fresh.