That is true. The only city I'm quite familiar with is New Orleans.
In 1960 it had a population of about 600,000 and growing. Gradually corrupt thugs took it over and today it has a population of less than 420,000.
Those with personal responsibility began escaping in droves in the '70's and now mostly live north of Lake Pontrartrain, a thriving , growing community with republican leadership.
The silver lining for N.O. is that the population seems to have stabilized with the murder rate about equal to the birth rate.