I am one of the culprits, and understand fully the argument to it. I don't own climbers, and the trees I hunt from wont allow it. I cant set up and take down a stand every day that I hunt.
I have gone in to find a stand set ten yards from me, or someone cuts a walking trail right over the deer run I'm hunting to get to theirs. It sucks, but its public. No one owns the trees or the ground, so you can get as annoyed as you want...but it will do you no good. If someone sets a stand in the same tree as me when I'm not there, tough cookies for me. Its kinda crappy, since there are lots of trees and areas to setup..but in the end everybody has the right of way. If someone is IN MY stand without asking, I have an issue. If someone takes my stand down to put theirs up, theres gonna be trouble. Public parking, if someone leaves their car unlocked can I just get in and sit in it? Its public right? No one owns the spot...so is it okay? Of course not. A tree stand is no different.
Now, its understood that if I'm not there, of course its okay to set up in the same tree as me. I have no say in it. Just dont move my stand. In the parking lot, you dont move someone elses car so you can park there.
My favorite way to deal with it, is to meet the people hunting if possible, get some phone numbers and if I wont be there, feel free to use the stand all you want once we know each other. You can pee all over, smell the whole place up, nap in the big scrape, tough for me. Thats public land hunting.
But at least getting to know who else is in there and sharing stands etc., will often turn the annoyance into comraderie. Sometimes not, but it is what it is.