It makes the dim objects hard to see. Nowadays it's quite unimpressive, and few children experience its spectacle unless, perhaps, they see the sky when camping in the summer. Yet many people never experience the joy of seeing a beautiful sky, something that drives many people to become interested in the universe in the first place. After all, it's not like air pollution or water pollution in the way it affects us. It is pollution, however, in the sense that it affects our environment by spilling light into a place where it doesn't belong.
Astronomers advocate lighting that is shielded with reflectors.
In this way, lower wattage bulbs can be used to receive the same illumination on the ground. Unlike most other types of pollution, cleaning up light pollution is relatively easy. The answer to that depends on what sort of observations we're trying to do. Probably photography, which uses ordinary light, is most affected. When it comes to using a big telescope as a camera, the reduced contrast is most noticable.