While the cause of many woes in our real society might be capitalism, in comic book Gotham its

• The Illuminati made up of rich folks in the city using zombie dudes to do their bidding (Court of Owls)
• The multiple Lazarus pits (2? 3? Not 100% there.) likely leaking into the water supply makin folks cray cray
• The portal to hell under the Sanitarium leaking evil all over
• The evil bat god trapped under the city also leaking evil all over
• The evil warlock who was trapped under the city leaking evil all over
• The evil swamp that spawned Solomon Grundy not too far outta town which probably is doing something

Like don’t get me wrong… I’m sure socialized housing and the like would help but grand scheme of things? Cities kinda fucked in a way that is far beyond conventional solutions, without a real way to unfuck it.

Also, for your amusement- https://en.wikipedia.org/wiki/Anarky