Agree about the vandals for sure. Well, cities, like most everything else have a life cycle. In fact, there are abandoned cities all over the planet. Many of them with no apparent cause or reason for their abandonment. But, back to Detroit; personally, I think as portions of the city become vacant they should be razed and returned to farm land. The scrapped buildings and such could be used to fuel electric plant furnaces or become land fill - something useful.
Many cities in Germany(and other places) have been doing fine for hundreds of years.. even thousands..
Could it be that you are ....WronG!...