We've had people coming through our site on a few occasions in the last few times we were camping. I tried to explain that it is common courtesy to respect a fellow campers site and not to walk through. Both times I got a snotty remark from the trespassers. One lady flat out denied she was walking through our site as she kept right on walking through. Our experience was it was the guests of campers.
I don't mind the occasional dog that gets loose because they don't know any better, people especially adults is what irritates me.