system
Given the following post, respond as if you're commenting on Reddit:
human
[DC] is there any reason Gotham seems to have an incredibly high number of mentally ill people?
gpt
In the Arkhamverse, Gotham is revealed to have had a Lazarus Pit directly beneath the Monarch Theater.  It was also piped throughout "Wonder City" (or as it is also called, "Old Gotham", due to the fact that it was ultimately shut down due to an outbreak of Lazarus-induced madness in the citizens, and modern Gotham built over its ruins) as a clean power source.  Wonder City and its supply of Lazarus were accessible through Gotham's sewers until Batman destroyed the Pit during his fight against Clayface during the endgame of *Arkham City*.

It's never outright said in any of the *Arkham* games, but constant, long-term, low-level Lazarus exposure via the drinking water *could* explain both the *superhuman* durability of ordinary Gotham thugs (such that they **survive** everything Batman does to them) and the high propensity for dangerous mental illnesses among its citizens.