Irrational? They think it is the only rational response left. It would be unwise to dismiss them as marginals or as misled youth. Many of them have an affluent and educated background and are capable of independent thinking and action.
Mumbai has not only been the gateway of India, but also the gateway for international terrorists and mafia members. Like New York in the US, Mumbai in India has been a tempting target for jihadi terrorists, particularly since 1993.