Argueing about how high is too high makes no sense. I had a friend almost die from a fall of no more than 8 feet. The point of the thread was WEAR A HARNESS.
I killed my oldest, biggest buck from 13 feet. SO WHAT! It was a high enough place to hang that particular stand. I personally hate heights and I have to re-acclimate myself to treestands every season but I love hunting enough to force myself deal with it. I've also been as high as 40 feet when it made sense to do so but I always wear a full harness. Sometimes it's necessary to get higher for a variety of reasons. I have a great spot on a steep sidehill. At 25 feet, I'm at eye level with one of the uphill better trails. Hunting at 12-15 feet there would be just plain stupid. Almost as stupid as not wearing a full harness.