Evangelism and the Ten Commandments

There is a great emphasis on the Ten Commandments in evangelism. The Ten Commandments are preached to give particular examples of sin that might show a person's need of forgiveness of sins in Jesus Christ. But should New Testament believers use primarily, if at all, the Ten Commandments as the standard of righteousness for gentiles and specifically New Testament believers? If so, why? The common answer is since the Ten Commandments are God's eternal moral law. The problems I see with this answer are: (1) it seems deep on the surface but underneath shallow; it does not seem to take seriously the continuity and discontinuity of the covenants, (2) it presupposes the tripartite division of divine law as moral, civil and ceremonial, when all of God's laws are moral in nature, (3) all of God's words either, written directly or indirectly, spoken or written, carries the same inerrant, inspired, infallible, authority, (4) it does not deal with the texts in the NT that seem to suggest a change of covenant (Jer 31:31-34) and law (1 Cor 9:21; Heb 7:12). Likewise, parsimony would suggest that, perhaps, the eternal law of God is simply the two commandments to love God and our fellow man.  Indeed, the Ten Commandments may be found in these two commandments, but one cannot from these two commandments extract the Ten Commandments. Theses laws are not clearly transitive.