As I understand it; the song is a long social commentary:
an a number of sujects revolving around the madhouses.

on the custom of pimping out the inhabitants of the asylum;
Of the custom of charging to view the inhabitants as an entertainment

that many of those there were suffering from (or because of) STD's

that those with genuine madness are usually harmless, but those who fake it for gain far from harmless;

And then the verses at the end are a prayer to not fall into madness.