I've not witnessed this hostility or violence, but as with all things there's probably some tiny fraction of the population that motivates comments like this one.

I have had non-dog owners speak pretty nastily to me, whether it's about my dog doing something natural (like defecating, which I carry bags for) or not realizing that areas are off-leash. I typically find the latter when I go camping (though there are certainly trails and campgrounds that are non-off leash this usually isn't about the dog itself, but the presence of predatory or endangered wildlife).

As a responsible dog owner, I check the beaches I'm going to, I check the parks (including trails and campgrounds) I go to, my dog is harnessed rather than collared, and my dog is properly socialized for both humans and animals (cats too!)