To me there is a difference between leaving a horse unattended and leaving a horse tied while you are within the vicinity. I leave my horses tied when I'm in the area, but I always make sure someone is in range where they could hear if the horse was in trouble. I do camp with horses, but my persuasion is to use a pen. It's pretty easy to throw up one of those temporary electrical pens and it seems more comfortable for the horses. Some places we go also have corrals since they're set up for horse camping. I don't consider leaving a horse tied while you're in a tent close by as leaving the horse alone, because you can hear if the horse is in trouble. We'll hear horses pawing the ground or rolling, etc.
I wouldn't leave a horse completely alone tied. Both of my horses have a known history of pulling back (the one mare I pictured did it before I owned her, my other mare did it once early in her training), but through retraining they can be safely tied. But I don't tie in halters that are completely unbreakable with no metal parts, and I always use a safety knot. That's because I believe any horse, no matter how solidly trained can pull back in the right circumstances.
I'm not saying it's morally wrong to leave a horse alone while tied and unable to escape, but I personally wouldn't do it. Where we live there are predators such as bear and mountain lions, and coyotes. I know first hand how quickly horses can get themselves into trouble as well.
Of course, we all do what works for us, and what we are comfortable with doing!
Far as a confirmed halter puller, I go for the cure.
Even if you are close, a horse can still get in a wreak, if his reaction to set back, and once a horse learns he can break free, he is more likely to do so.
There are some places where there are tie stalls, far as equestrian staging areas, but we also pack in to remote wilderness, and are not about to try and pack in panels!
I also go on hunting trips with hubby in the fall, where we at times tie up our horses, some distance from camp, go on on foot, and return after dark
When I started horses under saddle, after they were worked, they got tied up, alone in the barn, as part of the entire program
I rode other horses in between, or did household chores. Even now, every once in awhile, after I ride and horse and return home, they get to stand tied up , by themselves, for an hour or so
Some camp sites do have hitching rails, and our tent is not that far away, that I won't check on the horses, if something wakes me in the night, but I'm sure not going to sweat all night, lay awake, thinking that they might pull back and have a wreak. If they were to panic, at every slight noise! I would be darn sure there was a good reason,if they really started to panic, and send hubby out with a gun to check on things!