The problem with that interpretation is that you can't have "libraries turning into drug-infested, libraries turning into sex dens." because "drug-infested" is not a noun phrase a library can turn into like "sex dens" is. I also tried misinterpreting this comma as a comma between two adjectives, which doesn't work because "sex" is not an adjective.
Maybe "Libraries turning drug-infested, into sex dens" fits your interpretation better. Does it?