This is another one of Boiler's idiotic concepts that he can't let go of. It's intellectually cheap to say that A causes B without showing actual causation (rather than simple correlation).
As I've pointed out to Boiler, the more Chinese restaurants a city has, the higher the crime rate. So by Boiler logic, we should burn down all the Chinese restaurants. Problem solved!
Cities tend to be or become liberal because when people live in close proximity and there's a lot of economic activity, the ways that conservatism ass-fucks people become more and more obvious. People vote according to their own interests, and they realize very quickly that conservative politicians are just greedy money-grubbers who are happy to let a city deteriorate, as long as they can line their pockets.