You are naming places with really high violent crime statistics - for example Baltirmore is effectively locked in the top 10 most dangerous USA cities, usually in the top 5. It is not comparable to a city like Newark that is currently in the 50s. You would have to go back further then 10 years to say Newark was one of the most dangerous for violent crime.
Ironbound has always been fairly safe, including a decade ago. You have full time college students living there. South Newark is dangerous, and has always been dangerous.
Its not unusual for the UFC to visit NYC, Baltimore or Newark because they are playing at major arenas.