You bring up an interesting topic, Ian. As it happens, I never take a weapon with me except for bear spray if I will be in bear country, and it is clearly labeled for that purpose and well-known to residents and law enforcement in the areas where I carry it. I'd really pause before using it on a person, despite having already survived one random murder attempt. It's strong enough to cause eye damage.
Here in the Land O'Camo & Ammo (Northwestern US), friends and neighbors react with horror on learning I take no weapons with me. My 83 year-old neighbor was so concerned he offered a spare 9mm automatic from his collection before my last tour. Nearly all the outdoorsmen and hunters I know also pack self-defense weapons when enjoying the outdoors, but its not for me. People differ, but I really can't see any advantage to carrying a firearm or a knife intended for self-defense when cycle-touring, and would expect either to cause huge problems at border crossings and to likely work against me if I actually had to use them. William Sander's terrific 1982 book,
Backcountry Bikepacking, covers the topic of self-defense while touring very nicely and in some detail. A number of used copies are available through a Google search (or
http://www.amazon.com/Backcountry-bikepacking-William-Sanders/dp/0811722589 ). I've always enjoyed his writing on bicycles, and he gives a good summation:
Unless the situation warrants the use of deadly force -- an attack by an armed person being the only example the law would recognize -- and you are prepared to go through with it, and know how, don't even think about it.
The solo cyclist is vulnerable, but a bicycle or tent offer little in the way of defensive positions. Speaking for myself, I'd rather take my chances with avoidance and depending on the intervention and kindness of passersby in the event of trouble.
In order, my concerns when touring are:
1) Distracted motorists (talking or texting on cell phones or watching television on in-car monitors while driving).
2) Drunk or drug-impaired drivers.
3) Bored, liquored-up high school kids riding three to a pickup truck and looking for trouble/entertainment on a Friday night or weekends.
4) Being surprised when I'm asleep.
Weapons wouldn't help with any of the first three, and careful attention to stealth camping addresses the last. My small Swiss Army knife is a visible and non-threatening bright yellow, clearly oriented for camping use. Theft or robbery might be a problem, but I really can't think of any possession worth my life to defend, and I can't envision a situation where I could reach for a properly stored gun quickly enough to help.
A friend and I had the daylights scared out of us one time in the middle of nowhere when a couple drunks amused themselves by pacing us in their truck, tossing their empty beer cans at us while we rode on the shoulder. It was mostly just annoying until one of them accidentally tossed a full can and became outraged at its loss. At that point, they took the shotgun off the window rack and aimed it out the window at us -- cocked -- and paced us for awhile. We were scared to death, but tried not to react and they eventually got bored and took off. A gun or knife wouldn't have helped there.
You're right, Ian...having a friend along solves a number of problems, but can create others. I hope it works out well for you. At least you'll have companionship!
Best,
Dan.