Just imagine a scenario when two nuclear powered neighbors comes at a point of nuke exchange.The problem for the decision maker in a scenario where ballistic missiles have been launched at India, is that, there is no way of knowing if the missile carries a conventional warhead or a nuclear one. And for a country like India, which does not possess a reliable second strike capability, launching nuclear missiles immediately after detection of hostile BM maybe the only attempt at survival before the entire C&C network is wiped out.
Each and every BM launched against India would be countered by ABM. But those which would pass though would show its effect of whether being conventional or Nuclear tipped. Now in case of such a warfare, India too would be ready for any eventuality. So a nuke warhead would give India the very right of massive retaliation.
As far as C& C network is concerned, if you are aware of India's plan in this, you would have been least worried of it.