Gliphoeve, Kelbergen and other areas of the Bijlmer were so bad at some point that the police did not want to go there unless they went as a team. Robberies were on the order of the day, drug use in the subway stations and on the trains was so common nobody even noticed any more. The parking garages were essentially chopshops by night.
At a guess you have only seen the Bijlmer since long after the attempts to clean it all up have started. Maybe you'd believe my mom who had to get a large dog just to be able to make it from the shopping center to her house without being molested or robbed?
If you feel the Bijlmer is one of the most unique places NL has to offer then you are definitely part of some exquisite group of people with acquired tastes, the vast majority of the people that I know that have lived there and have moved out were happy to finally leave it all behind them.
The Germans are pretty unaware of how safe it is here, on the whole - they'll often explain to me a particular street is dangerous, or an area is bad - but honestly, if you're from any other country, it's a bit ridiculous.
I mean, feeling unsafe is bad - but to put it in perspective, one of my german friends lived in Coventry for a short while. On his second day there, he was beaten up at a bus stop for having long hair. That's what an unsafe area is like in england, which I'm sure is far more mild than most places in the world.