"Rottweilers are scary dogs. Their owners know this. Because that is why they got them.". What a sweeping generalisation. .
A lot of people buy certain breeds of dogs because they make them look "'ard", german shepherds, rottweilers, staffies etc. But similarly a lot of people buy these dogs because they like the breed and because in most instances they do make good family pets.
e.g. the staffy has been described as "the nanny dog" by some because of how good it is with children, and yet there are a lot of people who walk around with them on leads because they bear a resemblence to the other breeds of bullterriers that are not considered to be as friendly. I personally have had nothing but bad experiences with staffies. My dog was attacked by one a few years ago and I also know of several others whose dogs have been attacked by staffies. But my prejudice is born out of my experience, not out of the facts that are known about the breed, iyswim?
Similarly rottweilers have had a huge amount of bad press recently, and this is largely due to the fact that they are large, powerful dogs, and if in the wrong hands are capable of inflicting horrendous injuries. but if well trained/socialized/kept under control, they are no more likely to turn than any other breed of dog.
I personally wouldn't have a rottweiler as a pet because I would be unable to control a dog that weighs nearly as much as I do, but lots of people keep them very successfully without them ever causing severe injury to anyone.
If these dogs are under control they are no more of a threat to you than your spaniels.