Hi Brigid!

Don’t be so hard on yourself. One must make a distinction between INTERNAL and EXTERNAL judgment. When Our Lord says: "Judge not, that you be not judged" (Matthew 1:7/DRV), His dictum refers to one man’s judgment of another man’s INTERNAL state of soul. Only God can see the internal disposition. Was the external action done out of good or ill, out of friendship or fear, etc.? Man can see only the external result, not the internal intention.
On the other hand, WE MUST MAKE EXTERNAL JUDGEMENTS. We do this every day. A parent judges his child’s action unacceptable and punishes him. A judge or jury judges a criminal guilty. We judge that murder is wrong, that adultery is wrong, that theft is wrong. These are external judgments that we must make by God’s authority. Otherwise, the commonweal falls. We must judge the external action - we don’t want criminals walking around because they cannot be judged. God gives us that authority, as He established the state with its due authority: "Render therefore to Caesar the things that are Caesar’s" (Matthew 22:21/DRV).
This "judge not (at all!)" is a typical shortcoming of Modernist thought. It’s a way of saying that we cannot judge anyone else’s morals. We can’t say that adultery is wrong, or homosexuality, or theft. Of course, not even the Modernists really believe this. They don’t advocate the dismissal of courts. They don’t advocate the firing of judges. They don’t advocate letting murderers, thieves, and rapists go free with impunity. Obviously, even for them, EXTERNAL judgment is just and a necessity. They just judge differently, not in accordance with God’s law.
So what does this "judge not" dictum really mean? St. John clarifies it for us: "Judge not according to the appearance: but judge just judgment" (John 7:24/DRV). In other words, it is not judgment itself that is condemned, but UNJUST judgment. Catholic teaching is that just judgment is proper when it pertains to EXTERNAL judgment. For example, it is perfectly acceptable to judge an external act such as murder, to consign the murderer to the courts, and to punish the murderer if found guilty.
What we cannot do, as only God can do that, is judge the INTERNAL disposition. Perhaps the murderer was not compos mentis when he committed the murder. Courts can try to infer from external actions what might have
been the internal motive, just as a priest can try to infer the culpability of a penitent, but only God knows the true heart as a certainty.
So, when someone gives you that "judge not" quotation to suborn every kind of moral and doctrinal perversion, tell him that Moral
Relativism is not only an intellectually bankrupt idea; its real-life consequences can be deadly. Otherwise, we would have no justice in this world - just anarchy.
The Modernist notion of "judge not" isn’t scriptural at all, because it negates all other scriptural texts that illuminate the correct interpretation of St. Mathew’s passage.
Hope that helps.