The issue of self defense takes the discussion to a whole new place. It would hopefully be a very rare moment and to my thinking using a knife is absolutely justified. The application of other types of device is another argument that I will chip into only if STB wants to but I will say I disagree. The spray gives range and separation but the knife, if you have one and can use it, gives death and that stops an attacker a lot faster. It is down to will and training and some luck.
Any such spray device is as 'illegal' in many countries as is a pocket knife. Thirty years ago in Britain I was charged with having a pepper pot in my lunch box as an offensive weapon. The Police (however friendly an individual may be) on the whole can be very unfair in applying such parts of the criminal codes depending on their own experience and prejudice. I have worked with the Police in number of situations and I recognise the institutional mindset they can fall victim to. Often against bike-riders.
I have re-read my own posts and my own agenda is pretty obvious despite my first post being about the knife as a good tool no rider should be without so I don't mind where the thread goes or even if Carl moves it to 'off-topic'. Mind you no-one much else seems interested so maybe it will just die .