That's kinda the point, the felons have to be messin' with ya to make it a justifiable homicide. Go to Detroit wearing an expensive watch and walk through the wrong area, you will get ample felons messing with you. Heck, even the "wrong" NFL team jersey would do it.
Detroit LE apparently realizes the realities of their current situation. They are way outnumbered and every dead perp is one less gunning for them. The pro guide is to assure you find the right "wrong area" and have backup. Now, not everyone wants to hunt dangerous game and perform a public service at the same time, to each his own.