It goes without saying that a human space civilization will probably have methods of using and maneuvering asteroids, mass drivers on the Moon, and many other ways of shoving large masses around space at high speeds. These are all potential weapons, some of them with massive impact potential.

I expect that another part of such a space civilization will involve a lot of people keeping an eye on these things. Certainly any asteroids that are being moved will have lots of people watching the trajectories, but if you're talking small masses that can make a hole in the middle of the city, it isn't going to be easy.