Why is it a bad idea to walk around Africa at night? You might get mugged by a ghost
Did you have a bad experience in Africa at some point?
Africa is so full of danger and crime, I would never walk around at night
It's generally wise to avoid walking around in unfamiliar areas after dark, because there is a chance of crime in any neighborhood.  However, if you have never been to Africa, you should make statements about it being unsafe, because these could be construed as you meaning that all black people are criminals, or that the continent is somehow haunted.