Antinomianism is, in the words of that master wordsmith St Donald the Trump, ” not good”.
It is, strictly speaking, a heresy, a teaching that can be seen to absolve people from obeying the moral law, and thus, possibly, leading to licentiousness. Much was written about it and it had serious consequences, such as being condemned to a fiery death by the Inquisition. Those accused included Gnostics, Anabaptists, Cathars, Calvinists and American Puritans.
The theology gets complicated, but it seems connected to the “dualist” heresy that divides spirit and matter, the good spirit versus the sinful flesh, whereas Christianity holds that both are God-given. It is also seen as arising from the doctrine of grace and atonement of sins, which some distorted into “if God always forgives sins, why not sin?”
Ronald Knox writes a good deal about antinomianism (from the Greek “lawless) in his massive book about heresy Enthusiasm. Let me quote from his chapter on St. Paul’s letter to the Corinthians, widely known for their fornicating tendencies and “low life”:
“It seems clear that there were those at Corinth who adopted the antinomian attitude; who claimed that sexual purity was a Mosaic scruple which had disappeared with other Mosaic scruples. Christian life was a life of the spirit, not of the body; the Christian, therefore, should be above these materialistic taboos”. The apostles were forced to combat such heretical notions. They promulgated a decree that included the need to “abstain from fornication”. This precept was “to remain in vigour”. As Knox says: “The body, no less than the spirit, has to be dedicated to Christ.”
[Ronald Knox, Enthusiasm (Oxford, 1950),p.15.]