It's true that Johnny tried to make things right in season 2 by teaching mercy and honor.

But he does deserve blame for bringing Cobra Kai back to begin with and what Miguel became by teaching him the ways of the fist in season 1. And look what it did to the students at the end of the season. That's why he tried to change things in season 2.

And Miguel did choose to put himself into that fight by striking first like Johnny taught him. In that sense Carmen was right. Whether Miguel had a good reason for it or not. The risk of getting hurt are still there.

Alot of people are at fault for something. But that's what makes the show interesting.