Hello Fellow Christians,
The Bible says, "judge not" it doesn't say "discern not"
A person can discern and see that someone is a sinner, and yet not pass judgement. People can also pass judgement without using any discerning.
I think the difference is that in discernment, there's still hope for repentance and change and renewing and overcoming. In judgement there's sort of some kind of finality to it. God's not done with any of us yet. So, when we see someone sinning we shouldn't put some kind of finality to the sinner. We shouldn't assume that there's no chance for redemption or no hope for improvement and change.
In a way, I think that when Christ said, "judge not that ye be not judged" I'm sure He meant it as "don't give up hope on a person, so that folks wont give up hope on you" I don't think he meant for any of us to take off our discernment skills and trash them.
Peace
C C