You make a valid point that "fear" often drives much of what we do in the wild,(why else carry a 55lb pack), and to some extent that is a good thing. Keeps one sharp. Often gives one an edge. But most of us who have decided to go solo either on or off trail have to some degree already processed that issue. Cutting the umbilical of trail companionship is part of that "fear" issue IMHO. Being alone with oneself can be pretty intimidating.
I remember when I was in my mid 20's and did the Hurricane Island Outward Bound 30 day course. I was the oldest person in my crew, even older than the guides. Each person finds his or her own personal physical or emotional challenge during these courses, and one young crew member spent every day telling the rest of us how much she was looking forward to the 3 day sole experience. When we did go on our solos, she collapsed after 36 hours and had to leave to course an emotional wreak. She found much to her suprise that she could not handle so much alone time with her demons.
I think of her often when I talk with packers who do not solo and express shock and dismay that I do. Often these well meaning folk express their own "fears" when they tell me how unsafe it is, etc. When I wrote on this topic above that I have an unvarying routine that I employ to keep me safe, I was certainly aware that it might sound excessive or even fear driven. But, I do not live in a vacuum, I live with a most wonderous woman. To respect her feelings, I have adopted my rules. It gives her peace of mind. Certainly, I could violate those rules once on the trail, but then what kind of man would I be. And what would happen if even on a simple overnight, as Ryan suggests would certainly not get me killed, I deviated from my rules and did get into serious trouble. We all know that Murphy strikes when least expected. I do not think I would find it easy to explain to my wife that it was only an overnight and so did not qualify as a seriously threathening situation to follow the rules. "The path outside your door could sweep you up and take you anywhere -- even to Mordor." as Bilbo tells Frodo.
The one item which does not take up any room in my pack and which is truly ultralight weight and which is the key to my ultimate safety on any trip is the space between my ears and what I put there. If one is going to go solo, one owes it those we love and who support us in doing the "fearful" things we do that they may not appreciate or understand, to take wilderness 1st aid courses and any other course one can think of to hone our survival skills. Ultimately, confidence in my ability to survive and take care of myself is what my wife trusts -- the space between my ears -- and hence my rules.
I know that I have gone on quite a bit here, but there is so much more to this issue of Soloing: the how, the when, the conditions, the reasons, the benefits and the risks, that we should all consider more than the surface of this topic.