I'm of the opinion that self-defense should not be labeled as a crime. Usually, it's a situation of kill or be killed, and nobody would sit back and let themselves be harmed without putting up a fight at least.
For the school situation, it would have been better that they beat the guy and handed him to authorities(yes, I know how crapoy our justice system can be). I'm just not for jungle justice.
Yes, the policemen were there when they supported the setting of the guy ablaze. Before this happened, they killed one of our students still on the same street. So people were angry, and they burnt him.