Brøndby is a nice place to live, alot of friendly people, haven't really had any problems here since i was young and "troublemaker"
The only bad reputation we have is our Football hooligans and Brøndby Strand which used to be pretty rough place. Nowadays its pretty peaceful.
Most violent things that happend here are some local brawl between 2 groups (drugs) or when Hooligans goes to football game against FCK.
Hooligans fight other hooligans, not families or people who dont participate in that stuff.
The chance of you getting stabbed/robbed/whatever you're afraid of for no reason is low. very low.
Its bad business to rob and attack random people, the cops will just patrol the area 24/7 = no dope sale. And they are not interrested in that :D
Edit: Holy shit i made a book page =D