I once worked as an LEO in a "no-go area". Of course, it wasn't a no-go area - that's just bigoted propaganda. In Sweden, the police has a list of areas that are labeled as "vulnerable", which means that local police departments get extra resources to get a grip on crime in these areas.
The area I worked in was a place called Kronogården in the smallish town of Trollhättan. There had been a racist murder spree at the local school where a racist clad in a Darth Vader mask and carrying a sword killed a couple of non-white children and school workers just before. The murders had caused an increased rift between the locals and the police because the locals believed the police reacted too slowly to the situation in the school, thus letting their children die. There were conspiracy theories spreading about how the murderer (who was shot by police) wasn't really dead and was being protected by the cops.
The area was a drug selling hub, and the primary location for drug trade was in a run down community center just next to the school. The center contained a closed down library, two stores run by locals and the offices for the local land lord. That's where me and a colleague were supposed to be to "uphold order".
It became apparent that the drug sellers, and the likely perpetrators of most crime in the area, were a small gang of teenagers. They stood with us and we chatted until one of their customers came around. Then they excused themselves and slunk off, leaving their mates to keep an eye on us. Every once in a while some older brother of one of the kids came around and checked on them. It was kind of obvious that the drug selling had been passed down through the generations, the older brothers probably being a bit higher in the pecking order.
We arrested nobody for any offenses during our stay there. We didn't see any drug selling, although we were very much aware of it happening all around us. Police weren't interested in the drug trade at that moment, as the bigger problem was getting tempers calmed in the community. Our presence there was pretty much pointless.
Kind of a pointless story, but it does show that so called "no-go areas" are anything but.