Earth

The simple fact of the matter is that we don't really know what happened on Earth, or what's going on there now. We do know that pretty much every major city was obliterated by the orbital particle weapons. Yes, we're technically landing on occasion to acquire organics and resources that we just can't get anywhere else, and yes, that smacks of piracy, at best. But pirate or not, a lot of those missions don't come back, and we've heard some… odd tales, let's say… about primitive human societies being spotted. Some of them really primitive. At the same time, we know there's some active technological enclaves there — we catch the backwash of occasional signals, and there are even a few places where there's enough energy use going on to be observable from space.

Frankly, if we didn't have the occasional need for soil cultures, worms, and other drab necessities that just aren't available anywhere else, we'd probably just leave the place be.