It makes me wonder even more just what kind of a level 6 person were the masterminds of this project planning to create. A psychopath, nothing else. If someone has to kill 20000 girls to level up, it's going to affect the personality. For example, he wouldn't likely mind killing a bunch of scientists or politicians later. It seems quite self-destructive. But I suppose it still perfectly suits a technocracy like the Academy city.
In any case, an episode like this is building more background to why Mikoto was driven so crazy trying to save the sisters, since in Index we mainly saw Touma's side of things.