I disagree, because you state this as an absolute. Just as a kick to the head can end an MMA fight, it can end an attack on the street. If the situation is right, a high kick can be the right tool. I actively practice high front kicks to about chin height. A kick like that, delivered in the right situation, is more likely to end a fight than any punch I'm likely to deliver. I haven't figured a way to practice them safely enough (for my preference) with live partners, so I might not recognize the opening for them, but I want them in my toolbag.