Okay, I forgot about Chows. They are another inherently aggressive breed.
But heres the thing, in a broad view, about breeds that become aggressive (and I mean any breed, including cocker spaniels):
When a breed becomes very popular, usually due to a movie (dalmations in the 1960's for instance...I was also bit right in the face by one at 6 yrs old in 68) you see the very ignorant of society wanting to make money off the popularity by breeding and selling them, taking into account nothing about what the hell they're doing. You then see major health and behavior problems.
In the 60's, along with Dalmations, you saw many aggressive acts by german shepards because that was the breed du jour. Then came the 70's & 80's and doberman pinchers. Then the 90's and it was rottweilers and pit bulls. I worked at a vet for years and the #1 biter for many years during that time on the dept of health list was cocker spaniels. Why? Because of poor breeding skills by humans for expensive dogs. Look at chihuahua's.
My point is, all of the above breeds are great dogs (even pit bulls) but when you have human interaction of bad breeding, neglect, abuse, etc., you are going to see a prevalence of the popular dogs being aggressive.
Laws need to be strengthened for PEOPLE that mistreat animals and we'll see less and less of bad dogs. Currently the laws MAY contain a slap on the wrist for any abuse of an animal. It's a sin.