Dear Unni your argument suffers from serious errors in logic and assumption.
Your reasoning that the presence of parties like Shiv Sena and BJP is what keeps India sane from Islamic fanatics is erroneous.
If that was the case how would you explain India's existence before these parties. Or for that matter during numerous invasions by Muslim armies and for that matter a solid 200-year rule by the British. According to you theory India should have turned into Islamic nation and later a Christian nation due to recent British rule. None of them happened. India retains its integrating character as ever.
The fact is Shiv Sena and the BJP do not add up in the final count of what makes India. They are mere reactionary political entities. They are parties formed by opportunist politicians who hijack emotive issues to ride to power.
If BJP is serious on what it professes, it could roll the uniform civil code from day one it forms the government with help of alliances and sacrifice power and go to people. The reason they will never do it is because their priority lie in grabbing and keeping power as much as they can as any other party there is. You might give some thought over this.