I attended self defense classes and can say street fighting is much different.
First off is the obvious lack of rules.
Secondly the person you are fighting wants to harm you. Not just a black eye or a hurt jaw, they want you in the hospital or dead.
Thirdly and most importantly in my opinion is that they are nuts. What kind of person actually WANTS to harm anyone? You are not dealing with a reasonable, sane person.
A self defense weapon does two things.
One. Hopefully make it not worth it to try to harm you.
Two. If they are intent on trying anyway a self defense weapon gives you a chance to survive.
Times have changed. The animals rule the streets and the rule of law is a shadow of its former self. Protect yourself, no one else will.