I used to live in the heart of San Jose, CA and regularly took my dog to the large, busy local dog park.
Let me describe for you the “typical” owner of an intact male in urban (“East Side”) San Jose.
Usually the owners were young males, who did not seem to know the FIRST thing about dog training, let alone training their dog “well”.
Spiked pronged collar, on large athletic dog, often some sort of “staffordshire terrier” cross. Chain leash, wrapped many times around the hand (because you know, that makes you look like an experienced dog handler). Dog rearing against the leash, only partially in control.
Dog gets let loose in the dog park… and proceeds to wreak havoc, while his owner chills with his homies.
My small well trained dog got attached TWICE by intact males on separate incidences. The first time, there was a bitch in heat, and intact male was in the park as well, that male was running around FOAMING at the mouth, and attacked my dog as it happened to run by the bitch mr. balls was perusing.
Second time, another intact male became defensive of the water bowls, and bit my guy.
I know, I know, hardly a study, but I NEVER had a problem with the ball less dogs in the park. Those big males, with the hanging balls were the ones I had to watch out for. And I don’t think it is just because the dogs had extra hormones surging through them. I think it had more to do with the type of owner who choose not to “emasculate” their dog.
Sure, there are responsible owners out there, weary of the government, or negative health effects, and choose to not neuter their dog, but have them well trained instead.
But in my experience, usually the owners that do not bother neutering are the same owners that can not be bothered to train their dog.