We Christians do have a code of conduct which we are to abide by:
So I say, live by the Spirit, and you will not gratify the desires of the sinful nature. For the sinful nature desires what is contrary to the Spirit, and the Spirit what is contrary to the sinful nature. They are in conflict with each other, so that you do not do what you want. But if you are led by the Spirit, you are not under law.
The acts of the sinful nature are obvious: sexual immorality, impurity and debauchery; idolatry and witchcraft; hatred, discord, jealousy, fits of rage, selfish ambition, dissensions, factions and envy; drunkenness, orgies, and the like. I warn you, as I did before, that those who live like this will not inherit the kingdom of God.
But the fruit of the Spirit is love, joy, peace, patience, kindness, goodness, faithfulness, gentleness and self-control. Against such things there is no law. Those who belong to Christ Jesus have crucified the sinful nature with its passions and desires. Since we live by the Spirit, let us keep in step with the Spirit. Let us not become conceited, provoking and envying each other. (Galatians 5:16-26,NIV)
When we truly accept the salvation which God offers us, we are given the Spirit as an additional gift. It is through the Spirit that the motivations which originally controlled our actions (the acts of the sinful nature) are subdued, and a new set of motivations implanted. It is this new set of motivations (the fruit of the Spirit) which is to control what we say and do as Christians.
If another claims to be a fellow Christian, then he is to accept these motivations as the proper origin of his actions. However, if he does not claim to be a fellow Christian, then we are to reserve judgement:
I have written you in my letter not to associate with sexually immoral people - not at all meaning the people of this world who are immoral, or the greedy and swindlers, or idolaters. In that case you would have to leave this world. But now I am writing you that you must not associate with anyone who calls himself a brother but is sexually immoral or greedy, an idolater or a slanderer, a drunkard or a swindler. With such a man do not even eat.
What business is it of mine to judge those outside the church? Are you not to judge those inside? God will judge those outside. (I Corinthians 5:9-13a,NIV)