Ha,ha,ha I like the questions of bristle worms. Their great but if you over feed those things can get BIG!!!! And nasty and scary, I had one get over 15 inches in my 75 gallon tank! Can you say nasty! But they are good as a cleaning crew for sure but don't let them get too big, when that happens start using gloves to move your rock work.
as far as the worms killing other animals, what they're doing is going after tissue that is dead or dying. They detect it long before we're aware of it. Guilt by association. I agree with the others - they're invaluable cleaners.