I saw these pictures too, and was disgusted by them.
It might be possible to offer up reasons for their actions - mitigation and contextual rationalisation for acts of savagery and barbarism - but such behaviour cannot be excused, and the danger of offering such rationalisations is to give a partial excuse.
Its like saying its all right to lose your head- to abandon rationality, compassion, the law and justice; to lose yourself in instinctive savagery, indulge the animal within, translate a sense of grievance or injustice into lashing out - Just so long as there is a good reason for doing it.
Mob rule should always be condemned. No excuses, no rationalisations.