Detroit used to be pretty good and industrial, AFAIK. Now it's bad.
Usual attempts of checking questions like, is south african republic a shithole?
Yep, but there are worse.
End up with unbelievable fallout tier stuff like semiwild black tribes capturing skyscraper and shitting there so much, that they cant live there and have to capture one more skyscraper
Crikey, no. Not that I've heard of, and I've lived in, walked through or at least visited some of the worst places in the country.
/ police is afraid of going into lots of regions
A bit, yeah. The townships can be pretty damn scary and hard to police.
/ everyone not totally poor should better have electric razor wire fence or he will get robbed and killed by some black band
Depends on the region, but this is true to some extent. Particularly the very wealthy parts of Johannesburg AFAIK can be pretty bad. Ironically, you're often safer living in one of the better low-class areas. There's a heck of a lot of petty crime (e.g. garden tools tend to go missing. They're sold to pay for drugs, usually), but less of the serious stuff.
/ tied up with rubber wheel, splashed with fuel and set on fire for shits and giggles.
This has been known to happen. Often because of vigilante justice. Sometimes because you look funny. Sometimes because you sound funny. Sometimes because you look and sound exactly like anyone else, but you're from Zimbabwe so you must be a filthy criminal dog. It's pretty much entirely confined to the informal settlements, which are the places the police really struggle to handle.
Trying to find info in books did lead me to pretty same unbelievable stuff but with conclusion : they suffered from colonialism, so this is all justified.
Depends on the books you read. But yes, colonialism is/was/has been/I don't even know a problem.