There are different genes that code for different kinds of aggression in rats. Some rats may be great towards people but kill all babies of other rats, or they might be great to other rats and bite people, only bite when they have babies, kill their own babies when put under stress, males who only fight new males they haven't met before, males who fight all males, females who fight other females, so many different (and frustrating) types that stifle reproductive success and/or your ability to safely care for and harvest them. All of these types can be bred out of a colony, with proper use of outcrossing, inbreeding and selective breeding. However, it can be a very slow process, especially if the kind they have is to kill others.
As people already said, the best way forward is to start again. Most people have some issues with their rats, whether they notice or not, but your best bet is to go to another person who has good success breeding rodents in bulk for reptile food, and getting some babies from them. Third time lucky!
The kind of person who would be best to choose from, is someone who has multiple males and females breeding in one tub without fighting and killing, because you know they won't be baby eaters or hate all other males and females etc.
