I've always found that aggressive balls tend to start off as poor feeders--they're too defensive, and want to kill the rats with their teeth instead of constricting and eating them. <lol>

I also don't keep aggressive balls in my collection. Fortunately, all of my morphs are nice snakes, including my albinos. The woma-lesser I produced this season is also docile.
I suspect it has to do with people keeping snakes just for pretty, instead of pretty and temperament.