What a mentality professes is important, but often more important is where it necessarily leads.
Sola scriptura (especially in its adherence to covenant theology) leads to theonomy, for if we assume the Old Testament is still binding except where modified by the New, and this is assumed when all Calvinists argue for infant baptism, they use some form of the theonomic hermeneutic, then it is difficult to see how they don’t espouse some form of theonomy.
If they are consistent they must then affirm the theonomic outlook. At this point I would agree with Rushdoony and Doug Wilson that all law reflects one’s theos, and the theos that non-Theonomic Calvinists presuppose is the God of Scripture.
One of the few interesting points that the non-theonomic camp raised in the execrable Theonomy: A Reformed Critique is the multitude of contrary interpretations theonomy will create.. Tremper Longman said theonomy will eventually develop its own Mishnah. What he meant was you simply can’t say “We hold to the Mosaic law.” There are really not that many Mosaic laws, yet in the modern world there are myriads of situations not imagined by the Mosaic law. Therefore, theonomy really isn’t saying we are ruled by the Mosaic law, but by interpretations of the Mosaic law.
Here is where it gets interesting. Whose interpretation of the law is valid? How will we know? The answer to that reasoning process will create yet more interpretations. As any theonomist knows whose studied case laws–it’s not so simple just to say, “We follow the law of God.”