George S. Ledyard
Basically, I think that someone who pursues Budo as a Path has an obligation to use those skills to protect folks who are not capable of protecting themselves. What else is your training for?
That said, you have to be realistic and understand that ANY time you intervene it could instantly and without warning become a life and death matter. If you don't go into it with that mindset, don't intervene. Also, in a violent confrontation, it makes no sense to intervene unless you actually have the skills to back up your words.
There are so many thoughtful things written in the post that it'll be embarrassing to voice out dissent. And logically I agree totally with mr ledyards post, do budo? Protect others. However don't do it if you can't and don't do it without back up.
However, I think though we do budo as something tangible in our training, the spirit of budo exists regardless. It also remains absent regardless. The spirit of budo is upon your true self to manifest.
Thus having a spirit of bushi/budo the question or choice to protect others is moot. You either do it or you don't have it.
There are situations where categories of protectees exists (is that even a word) that require you to prioritize but all in all, it's your responsibility to protect the right.
Logically, do it when you can win. But when is that ever certain? A seasoned combat veteran gets stab by a kid after a long campaign. An undefeated warrior, gets run over by an assailant who lost earlier... Such is the world of violence. Thus you can only do your best and hope for the best. A famous general said something along the lines of an imperfect plan today is better than a perfect one tomorrow, essentially saying sometimes time is of the essence and we can't be 100% of anything. Having said that, entering training, getting experience are ways to improve your chances. But a gamble it remains.
Waiting for back up. Well that's all well and good when you're in uniform. In a mob... You do what you have to do.
Finally of course, a smart warrior is a live warrior. A brave warrior is a dead one....