ck - I think you hit it spot on. In the book of Hebrews, it tells us that we are to confess our weaknesses to one another, that we are to support one another daily so that the deceitfulness of sin doesn't overtake us.
Well, if I don't "judge" what someone's weaknesses are, then how am I gong to support them to overcome their particular weakness. Trust me, if you come up to me and simply say, "Hey, krellin, have a good day, don't sin..." versus saying to me in knowledge (and "judgement") "Hey, krellin, have a good day, stay away from your alcohol triggers, don't drink...call me if you get in to trouble..." ONE of those will be much more affective. One of those implies that you are "judging" me for my weakness...but I would much rather have a loving brother loving me and calling me out than have a brother NOT judge me for fear of violating some principle, and instead stand by and watch me self-destruct.
The mis-insterprtation of "judge not" is one of the most aggregious and offensive things to me...because it means people stand by and watch others fail. And WHY? Because they are afraid of being judged themselves? Bah....that's called selfishness...
Similar note, Paul discusses the body of Christ and says that all parts of the body are equal..the eye, the legs, the ears…whatever, we are all equal in the body. AND, when one part of the body grieves, ALL parts of the body are to grieve. So, there again, if I am failing in a sin, you, my brother, are supposed to grieve with me and be in pain with me. And, again, this cannot be done if you are standing to the side, arms crossed, not involved because you are afraid of “judging” me.