One useful little concept that a friend and I have is that of the antiskill. Like a normal skill, an antiskill gives you both the ability and the affordance to do things that you wouldn't otherwise be able to do. The difference between a skill and an antiskill is that a skill gives you the ability and affordance to do things that are positive on net, while an antiskill gives you the ability and affordance to do things that are negative on net.
For instance, my friend believes that dancing is often an antiskill, because it gives you an affordance to dance rather than have interesting conversations while at parties, and he considers having interesting conversations to be much more valuable than dancing-- therefore, knowing how to dance serves primarily to enable choices that are bad on net.
I disagree with the specific point in this case, but I nevertheless think it's a good example because it illustrates another key principle of skills and antiskills-- whether something is a skill or an antiskill is context-dependent. If dancing will largely prevent you from having interesting conversations, it may well be an antiskill-- but if you go to a lot of nightclubs where loud music makes conversation difficult, knowing how to dance seems very useful indeed!
Another example is the skill of knowing how to fix computers. In many respects this is very useful, and can indeed lead to a profitable career in IT. But-- as I'm sure many of you may have experienced-- having your friends and family know that you know how to fix computers can be very negative on net!
Overall, I find the skill/antiskill framework quite useful when it comes to navigating what sorts of skills, abilities, and knowledge I should acquire. Before choosing my next priority, I often pause to think:
- What affordances will learning this give me?
- In what contexts will those affordances be most relevant?
- Will this be positive or negative on net?
Using this framework has enabled me to discern strengths and weaknesses that I had previously not considered, and in some cases those strengths and weaknesses have proven decisive to my planning.
I agree with your conclusion but not your reasoning. If you're already in a self-defense situation, martial arts training probably makes fighting more attractive, and therefore more likely relative to flight (if possible) or freezing up (if not). The confidence you're talking about does make fighting less likely in general, but it does that by reducing the chance that you'll get into a threatening situation in the first place: unless you're going around looking for fights, that implies someone else threatening you, and most of the people that're interested in doing such a thing are going to be looking for soft targets.
Also, in such a situation, most of the sources I've read say that you're more likely to avoid death or serious injury if you do fight back.
On the other hand, you do run a nontrivial risk of injury in training; martial artists are more likely to be injured on the mat than on the street. Most of that comes from being a high-impact athletic activity rather than from the self-defense motive, though, so choosing a non-defensive martial art probably won't help you much. (Anecdote time: I've been hurt more doing fencing, which is defensively useless, than doing jujitsu, which isn't.)
I don't understand the point of fencing. From the videos I watched it is a very ungrounded activity with the contests hoping around instead of being a position that trains the kind of body language that you want to have in your normal life. It seems doesn't look like fluid movement. It looks more like it's about the guy with the fasted reaction time winning.