John Frame has responded, and his reply has been posted online: "In Defense of Christian Activism." Here is an excerpt:
Michael Horton's article in Christianity Today, "How the Kingdom Comes" is a typical popular presentation of this position. He emphasizes that the Kingdom of God comes by God's power, not ours. He points out that Jesus in the New Testament does not commission his people to destroy unbelievers with the sword. So "there are no calls in the New Testament either to withdraw into a private ghetto or to 'take back' the realms of cultural and political activity." The church exists within the world as a community of word and sacrament, but does not seek influence in the larger society. He says, "there is no 'Christian politics' or 'Christian art' or 'Christian literature,' any more than there is 'Christian plumbing.'" Then he urges the church not to try to be like the world, or to make the world into something like the church.
There is much truth in this position. Certainly God does not call us today to destroy unbelief with the sword, as God called Joshua to destroy the pagan inhabitants of Canaan. But one can certainly renounce the use of the sword against unbelief without renouncing Christian activism in general. Christian activism, remember, is simply the attempt of Christians to improve the general society. Especially today in the democratic west, that can be done by many lawful means, without violence.
So Horton confuses the question of whether we should use violence with the larger question of whether we should seek to influence developments in society. I believe he confuses other questions as well.