If it gets big enough, it could cause a soft-fork. But that's a much different/smaller problem than a hardfork, and unlikely to occur (since miners would presumably get their act together before it got to this point).
If half the network decides that blocks containing SD transactions are valid, and the other half decide they are invalid it would indeed be a hard fork.
There's no guarantee that it would go your way either. The majority of the network might just continue processing those transactions and ignore your blocks until you get your act together.