One thing we can all admit is that we are more antinomian than we should be.
A very wooden definition of antinomian is to be against (anti) God's law (nomian).
Every child of God has more than just a little bit of an adversarial spirit toward the law of God. A few virulent strains of unbelief still remain in us which make us suspicious of the goodness of God's law. Even if we sustain the strong conviction that God's law is "holy and righteous and good," as Paul says in Romans 7:12, we still find ourselves not doing the very thing we know we should do, as Paul laments in Romans 7:15. In this way our theological convictions may not be antinomian, but our obedience, weakened by the flesh, still is.
But this is not how the word antinomian is ordinarily used. It is ordinarily used to describe those whose theological convictions are "against the law." For example, if someone claims to be a Christian but openly disregards God's moral law as revealed in the ten commandments, they are an antinomian by theological conviction. They think they are both bound to God and free from God. Bound to him in grace but free from from his rules. Antinomians emphasize justification (full pardon of sin) but they do not emphasize sanctification (progress in holiness).
Over the years I have met more than one easygoing church-goer who thinks he is not obligated to worship God on the Lord's Day (contra the 1st & 4th commandment). I have met church-going couples who think God could not possibly be angry they are cohabiting outside of marriage (contra the 7th commandment). I have met others who think collecting welfare checks from the government is a noble way for able-bodied people to earn a living (contra the 8th commandment). I have met pastors who think the occasional reading of a children's book instead of preaching on Sunday is a right and acceptable form of worship (contra the 3rd commandment).
To be fair, however, the reason there are antinomians in the pew is usually because there are antinomians in the pulpit. When a preacher affirms the importance of the moral law in his ministerial exams but then refuses to exhort his congregation to obey God's law in his preaching, his ministry becomes a breeding ground for antinomianism. Justification is emphasized (pardon) but sanctification is downplayed (holiness). Adult disciples of such a ministry unwittingly double this dilution of God's moral law which leads to disturbing outcomes in the next generation: (i) children who learn that God is always pleased with them no matter what they do, contra Hebrews 13:4 (ii) children who scarcely know anything of the fight against sin because they have not been challenged to obey God's commandments, contra Hebrews 12:14; and (iii) children who can not delight in God's forgiving grace nor his empowering grace because their soul has never felt the impossible weight of his commandments, contra Ephesians 1:6-7.
To deal firmly and resolutely with antinomianism the Christian must understand that the work of Christ was not to destroy the law, but to fulfill it (Matt. 5:17). Finally, and for the first time in history, the law blossomed with all its perfections in the obedient human flesh of the God-man, Jesus Christ. Thus the law is fulfilled. Its demands have been met. It no longer condemns the redeemed race of men, namely, those who have come to share in Christ's obedience by faith.
But this does not mean we are no longer called to the observance of God's law. Jesus said, "If you love me, you will keep my commandments" (John 14:15). Having been first loved by him, we now love him (1 Jn. 4:19). Our love for Jesus is manifested in our will to conform to his commandments through our obedience. Observing his law then is not a means of justification but it is a rule of life where our lives begin to fit the shape of Jesus' own love for God and men. After all, we were "predestined to be conformed to the image of his Son" (Romans 8:29).
As we are now seeing, the most potent truth in overcoming the lie of antinomianism is our identity and union with Christ. Think of it this way. When we come to God through faith in Jesus Christ we do not come and take grace from God to cover over our sins. Nor do we come to take rules from God to straighten out our crooked lives. When we come to God through faith we come to take Christ himself! The benefits of Christ cannot be separated from his person. No one can come just for pardon. No one can come just for wisdom. To come is to come for the whole Christ, the person, to enter Spirit wrought union with him, to belong to him, to receive all that is his - including his righteousness for our justification and his holiness for our sanctification. The justified must be sanctified for such is the reality of union with Christ.
The great error of antinomianism is the separation of the work of Christ from the person of Christ. The doctrine of union with Christ slays this error utterly. To be in Christ is to become like him, loved of the Father as adopted sons and set apart unto heaven's holiness through his newness of life.