They removed the bottom part of the ladder stand for a reason.
I would never use anyone else's stand, even on public property, unless I talked to the owner first. I feel empathetic with subjects like this. I think how I would feel if someone used my stand without permission.
I'm not sure what the law says. Whether the stand is open to all to use if it's on public land. It still does not make it right. Courtesy and respect for fellow hunters is in order here.