I think the general concept and necessary factors involved in running, make it unavoidably rude if done in public.
Runners need to run at a steady pace, not stopping and starting, they are generally trying to cover a distance in a set time or beat a personal best and don't want this disturbing.
Having to slow, shout out, stop or move around other people is difficult to do without ruining that pace or flow or that set time/personal best... and so many don't bother and instead run up behind people startling them, or pass too close etc etc.
Combining runners with other pavement/path users is a recipe for one or other set of users to get pissed off.
As a wheelchair user with no rear visibility and little ability to turn my head (I have to stop and turn the whole chair), having some heavy breathing feet pounding up behind me or appearing suddenly is quite startling and not fabulous for someone with a heart problem.
If I am walking a dog, I'd rather they called out and passed MUCH further away than they normally do - running up behind or head on at a dog is, for the dog, very threatening and frightening and many dogs will react badly to that, particularly if the runner stares at the dog or owner or shouts at them (just adds to the threat).
But there are other pavement users who are bloody annoying too... people who walk in a big group, clogging up the pavement, people with headphones in or phone zombies who despite me calling out, have no idea I am there, people with toddlers who grab at my chair or at my dog as I pass...
World is full of annoying folk and some are more likely to annoy than others.