Here's the big question; is GANTZ a force of good, or evil? Assuredly, killing the aliens, whom really have not been bothering people, could be considered bad (but cool), but on the offhand, GANTZ is giving those whom died a second chance at life. For every criminal that gets recruited, there are a bunch of decent people as well.
Kurono is in a good position to stop GANTZ forever, if he should take such a route; he no longer has the brain-explosive, is no longer summoned to games, and has hidden memories of GANTZ's games. However, just because he can stop Gantz doesn't necessarily mean he should; what do you lot think?