There is a difference between judging that someone is going to hell and warning them of the possibility of hell. Catholics know that they are not to judge someone’s soul. To do so is to try to be God and I can only firmly warn you that this is not a good idea. We are unable to judge the interior of one’s soul, only God can do that. You mentioned an atheist earlier. I knew a “tried and true” atheist that was in a serious car accident. As the car was crashing, she cried out, “Oh God, please help me!!”. She lived and had a profound conversion experience. Up to that point in time, any one of a number of Christian evangelical types would have told her she was going to hell— but see, in her heart she really did believe in God. It was only in that moment of desperation that she realized in her mind, what her heart had known all along.
That does not mean that evangelization is not necessary. We in the Catholic Church are told that the Church exists to evangelize. Anyone with even a marginal knowledge of history knows that the Church evangelizes and, in my opinion, the “you’re going to hell” technique has been the most ineffective tactic that the Church ever used. Yes, we did that routine many years ago and lost a lot of Catholics because of it.
As Christians, we should follow Jesus’ example. Jesus’ first words of public ministry in the gospel of Mark were “This is the time of fulfillment. The kingdom of God is at hand. Repent, and believe in the gospel.” We also have His example of the adulteress that was going to be stoned and He said “Let he who has not sinned, throw the first stone.”. Jesus knew how to effectively evangelize. Although He was in the position to condemn, which we certainly are not, He always just gave the message of repentance, turning toward God, how to walk in His way, etc. He wasn’t screaming at the people “y’all are gonna burn in hell!!!”.