I don't think either party came off well.

I have a dog that I sometimes let off leash if the trail is empty. If someone comes along and asks me to put my dog on leash - I comply. Because you know, those are the rules.

Ms. Cooper could have politely apologized for not following the rules and put a leash on her dog.

OTOH, thanks to the dialog you posted, which was not made available generally, it's obvious that Mr. Cooper was not innocent either. Who implies that they may give something harmful to a dog? Even if you don't like dogs, why harm it, when it's not even the dog's fault for the bad behavior - it's the owner's responsibility.

Finding out that Mr. Cooper has apparently gotten into it with other dog owners makes me wonder if he has a screw loose.

None of that excuses Ms. Cooper from making racist comments, however. Again, a reasonable person, when confronted by an anti-dog nut, would calmly and quickly grab her dog and just get the heck out of there. Hanging around making a scene was not a wise decision on her part. And making racist comments... so not OK. JMHO