Robin with all due respect I would say that is the great temptation of any society that tries to use the civil authority to enforce the civil laws of Israel upon society. True Posties see the change wrought upon society via the gospel and changed lives Theonomic Posties see the Christianizing of society via the use of the law: Again I'll quote Ray Sutton:

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Many sound Christians have exercised influence there [i.e., the political and social arena]. They have held political office. But more often than not they have not ruled by the Bible, particularly God's law. Rather, men such as Abraham Kuyper believed in the rule of natural law, even though he implemented some fine Christian legislation. So, after Kuyper the present age of decadence began. Why? Because the Bible and God's law were not set up as the rule. Christians ruled, in other words, but they did not establish Christian rule, namely under God's Law.

Sutton's quote is illustrative of those who say that they want to change via the gospel but in actuality once they are established into office they want to impose the law of God upon the unregenerate. This isn't the same as the traditional postmillennial view which saw the gospel as the vehicle that changed the culture.

Boettner:
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We have defined Postmillennialism as that view of the last things which holds that the Kingdom of God is now being extended in the world through the preaching of the Gospel and the saving work of the Holy Spirit in the hearts of individuals, that the world eventually is to be Christianized, and that the return of Christ is to occur at the close of a long period of righteousness and peace commonly called the 'Millennium.' It should be added that on postmillennial principles the second coming of Christ will be followed immediately by the general resurrection, the general judgment, and the introduction of heaven and hell in their fullness.

Peter

If you believe what you like in the gospels, and reject what you don't like, it is not the gospel you believe, but yourself. Augustine of Hippo