No, you're wrong. You're acting as if miners have a choice. They don't. They must make blocks that the network accepts, or they're not miners anymore. If they make invalid blocks, *they* are splitting the chain - not the softfork. Furthermore, their invalid blocks don't constitute a real chain: every time the valid chain gets ahead, all the old nodes will drop the invalid blocks and those miners will start over, with huge losses. The only way they can avoid this, is with a counter-fork.