The main gist of it is absolutely correct: if you are attacked, you have the right to defend yourself (NB: be aware of the laws in your state regarding appropriate levels of force and if there are any caveats such as a duty to retreat, etc. – not every state’s laws are as cut and dried as Arizona’s). If you started the altercation, not so much.
This is something I find bleeds over into almost every encounter I have with other people. If you (or, far more likely, they – I am the soul of tolerance and politeness) don’t make a deliberate effort to be difficult, rude, pushy, belligerent, etc., chances are the interaction will go smoothly and pleasantly. Or as Will Smith said in Men in Black, “”Don’t start nothin’. Won’t be nothin’.” Let’s face it, people bring most of their troubles on themselves.