While it's easy to quickly speculate that the only purpose of 100,000 "unregistered" SIM cards is to "do bad things", I have to wonder: Why does a SIM card need to be registered to begin with?
SIM cards need to be registered so that the Indian police can track criminals. Personally I disagree with this. Criminals will disregard this law so it will usually only apply to law abiding citizens. Try explaining that to the Indian CBI though...