India is a conglomeration of nations, of ideas, of religions, of beliefs and of ways of life in constant flux. The very act of trying to define what India stands for, destroys the idea of India. Because any definition would be just a snapshot in time, from a particular point of view, of an evolving organism.
Various movements try to define India according to their own viewpoint and try to influence the rest of the population with the ideas that they personally espouse. Some of them try to bring about change with peaceful means while others resort to violence and hooliganism.
As long as you hold a belief and are using civilized democratic means to spread it, I have no problem with you. But when you use violence or hooliganism to enforce your point of view on others, I would want the law and order machinery to track you down and penalize you to the full extent of the law. I would expect the government of the day to prevent you from violating the liberty of others, but I would not want you banned.
What does banning an extremist organization achieve? Are they reformed overnight by a ban? From a practical point of view as well, banning an organization would just result in sending it underground and resort to furthering their cause through clandestine activities. I would rather have them above ground and monitor their activities and try to counter their arguments in a civilized way.
I am against banning any organization whether it is SIMI or the VHP or lately the Shri Ram Sena of Mangalore fame. I would not deny them the liberty to preach their ideas and viewpoints without resorting to violence.
Voltaire is credited with the saying 'I disapprove of what you say but I will defend to death your right to say it.'