If the ‘zombie apocalypse’ ever starts, the people coming off their meds will be interesting, to say the least. No malicious intent will be necessary for an army of people who are really messed up...
It was just such a scenario that helped ruin Asbury Park, NJ. In the late 60's, they closed the local mental hospital, and a lot of them were section 8'd into housing or just plain let out. They turned a seaside mecca into a Carnival of Souls -type empty shell.
Obviously it's more than just the psychos - it was the druggies and the nearby downtown "civil unrest" of the 60's, let's just say. It's kind of like the pics you see of downtown Detroit.