The following article contains spoilers from Action Comics #1047, on sale now.
The world is adjusting to not only Superman's return but also the Warworld hanging over their heads. Action Comics #1047 (by Phillip Kennedy Johnson, Riccardo Federici, Lee Loughridge, and Dave Sharpe) made it clear that the people of Earth are concerned about the potential damage the population of Warworld could do if they decided to go rogue. However, it is not the people who they should be worried about, but the Warworld itself.
In their orbit right now is a planetary body that is more or less equal to the size of the moon. Never mind the people it's carrying, the physical effect the Warworld's presence will have on the Earth could be catastrophic. Having another moon-sized object in orbit would not only disrupt the gravitational pull the Earth has enjoyed but it would also cause multiple natural disasters as a result.
Logically one would say that Superman wouldn't be reckless enough to endanger the people of Earth in such a way. The Warworld would have to be a good distance from Earth for the sake of safety. Unfortunately, numerous parts of the comic indicate that this is not the case. When the Warworld appeared, it was even more visible than the moon, an indication of how close it was. Then, Lex Luthor's trip to Warworld showed that it was only a few minutes away via launch from an orbiting satellite. So by all accounts, it is absurdly close to the Earth.
One can understand Superman's reasoning for allowing it to get so close. There could be numerous projects to reverse engineer Warworld's tech for the benefit of Earth, perhaps even propelling humanity into a new age of technological development. To do so would require the planet to be close by. More importantly, some of its people have expressed an interest in making Earth their new home, the trip shouldn't be too long for their sakes either.
However, the natural consequences of bringing another celestial body into Earth's orbit could be dire. A heavy disruption to the Earth's gravitational relationship with the moon could result in severely higher tides, eroding coastlines until eventually flooding and wiping out major cities. The more immediate problem would be frequent tsunamis, increased geological activity resulting in earthquakes, and possibly volcanic activity. Earth already has several super volcanoes that could wipe out the planet's surface, if the Warworld's gravitational pull affected those, Earth would be done for.
It seems insane that Superman would be so short-sighted. Even if he didn't think about this, he has brilliant friends and allies who would have pointed out the risks. The most likely reason why this hasn't been brought up yet might simply be due to an oversight by the writer, ignoring the cataclysmic effects of bringing the Warworld that close to Earth. Or perhaps it will become a problem later down the line, but chalking it up to a blunder on Superman's part seems incredibly out of character.