|(photo by Michael Taylor)|
Right away we must say this is illogical, since theonomy, properly understood, holds to justification by faith alone; one does not obey God's law in order to be saved, but rather God grants one a desire to obey God's law after he has been saved. That is, a believer obeys God's laws after being saved out of a heart of gratitude.
But beyond this, anti-theonomists attempt to "connect the dots" between theonomy and the Federal Vision by arguing, "see, some members of the Federal Vision are theonomists." Well, some members of the Federal Vision are non-theonomists as well.
And what's really embarrassing for those who make such anti-theonomic arguments is the fact that the men who perhaps had the most direct influence on the Federal Vision are two non-theonomists (Norman Shepherd and N.T. Wright) and two former theonomists (James Jordan and Peter Leithart).
Furthermore, consider the fact that five contributors to the anti-theonomic book "Theonomy: A Reformed Critique" have signed the "Presbyterians and Presbyterians Together" document. This document is for either Federal Visionists or Federal Vision sympathizers in Reformed circles.
(Those contributors include Tremper Longman III, John Frame, Dan McCartney, William S. Barker, and Samuel T. Logan. See the signatures here, and for a critique of this document, click here.) 
Granted, we can only really ascertain whether one position or another leads to Rome by Scripture. And by Scripture, we can in fact say that rejecting theonomy is a Road to Rome.
Roman Catholicism is fundamentally equivalent to the theology of the apostate Jewish religious leaders during Christ's earthly ministry, since both groups deny the doctrine of justification by faith alone and elevate the traditions of men over the Word of God.
So we can look to the Gospels for insight into what constitutes a road to Rome. And the apostate religious leaders during Christ's earthly ministry were anti-theonomists: notice how Christ indicts them for nullifying God’s command to honor father and mother, as well as God's command “Whoever reviles father or mother must surely die” (notice that this command entails a civil penal sanction.):
1Then Pharisees and scribes came to Jesus from Jerusalem and said, 2 "Why do your disciples break the tradition of the elders? For they do not wash their hands when they eat." 3He answered them, "And why do you break the commandment of God for the sake of your tradition? 4For God commanded, 'Honor your father and your mother,' and, 'Whoever reviles father or mother must surely die.' 5But you say, 'If anyone tells his father or his mother, "What you would have gained from me is given to God," 6he need not honor his father.' So for the sake of your tradition you have made void the word of God. 7 You hypocrites! Well did Isaiah prophesy of you, when he said: 8"'This people honors me with their lips, but their heart is far from me; 9in vain do they worship me, teaching as doctrines the commandments of men.'" (Matthew 15:1-9).Thus, rejecting theonomy is a road to Rome; for these same apostate leaders whom Christ indicted not only largely rejected God's law as a standard of obedience (they broke God's commands for the sake of their traditions), but they also rejected salvation through faith alone apart from works (which explains why they never had a heart change; their hearts were far from Christ).
In short, they largely ignored God's law as a standard for sanctification, and perverted God's law to make it (or their own traditions) the basis for their justification. This is exactly what Roman Catholicism and the Federal Vision does.
Antinomianism (i.e., anti-theonomy) and works-righteousness go hand-in-hand. Rejecting theonomy is a road to Rome.
NOTE: We are not saying that everyone who does not identify himself as a theonomist is on the road to Rome. All true Christians have the law in their hearts, and as such at the most fundamental level they are theonomists (after all, theonomy in the general sense simply means "God's law").
However, what about the rejection of theonomy as it is commonly understood to mean (that is, that civil governments are required to enforce much of the Older Testament judicial law)? We will just say that the rejection of God's law in any sphere of life--for example, family, church, and state--theroretically puts one on the path to Rome, since Roman Catholicism is premised on rejecting God's Word for man's traditions.
However, God's grace keeps those who are his from taking a path to Rome to its logical conclusion. And, no professing theonomist who is a true Christian is consistently theonomic in any sphere of life, and no professing non-theonomist who is a Christian is consistently non-theonomic. We imagine some Christians who are not professing theonomists are more consistently theonomic, that is, they uphold God's law in all areas of life, than some Christians who are professing theonomists.
 While there is a problem of the Federal Vision heresy in theonomic circles (just as it is a problem in non-theonomic circles), according to someone we know,
“From what I have read and understood, most evangelicals who embrace Rome or Eastern Orthodoxy for that matter are generic, eclectic or even dispensationalists from Dallas Theological Seminary. They have not had any influence by theonomists whatsoever. Evangelicals become Roman Catholics because of marital reasons and all sorts of other ecclesiastical reasons or personal preferences, such as Divine Liturgy, which have nothing whatsoever to do with theonomy. They don't even know what theonomy means.”
Theonomy does not Promote Salvation by Works (part 1, part 2, part 3)
Brian Schwertley defends R.J. Rushdoony's View of Sanctification (part 1)
Greg L. Bahnsen versus Norman Shepherd and the Federal Vision (part 1)
The Covenantal Orthodoxy of Daniel Ritchie