score:7
There is a difference between condemning and being discerning. One is using the good judgement God gave you, the other is judging in the place of God.
It should be clear that Christians are supposed to be "as wise as serpents but as gentle as lambs. ". Throughout the NT, we are warned to avoid false teachers and cast them out of our midst. We are to encourage and rebuke our brothers
But note the context- in the cases where we are to use discernment, it is in a personal, relating body of believers. We are not called to be God's policemen, forcing a system of morality on unbelievers. Rather, it is a privilege to be subject to the discipline of God - for after all, he only disciplines those he loves.
If a brother is calling himself a Christian, he invites discipline, rebuke, and encouragement. He sees it as a way to be the person God created him to be. If not, there is no use in casting your pearls before swine.
Upvote:2
Christ himself says, 'Judge not lest ye be judged', and in another place, 'The same measure by which ye measure shall be measured unto you.'
It's not unreasonable to assume that if you are condemning other people, you are committing a sin, as Christ himself even says that he did not come to condemn anyone, but because they stood condemned already.
So the answer is, if you know their heart and know that they reject God it would be irresponsible for you not to warn them that rejecting God will cause them to be condemned. But given that I myself do not know anyone's heart, hardly even my own, I would say that to do so is at the very least presumptuous for two reasons.
But merely proclaiming this - that those who do not confess and believe will be condemned - is no more sinful than declaring that those who fly into the sun will be consumed in plasma fire.
The consideration must be the reason for proclaiming it and to whom it is directed. Rarely do we use such a verse in an objective fashion; it is almost always directed against a particular person or person(s) we know to be unbelievers. This is prideful and dangerous.