I think you will find that Jesus meant the contempt that can underlie condemning another as a fool...it does show a degree of judgement to call someone stupid and it can undermine their self image, if not our perception of another person.
It was the unloving contemptuous meaning held in the words sometimes that Jesus was censuring. He teaching is all about 'Love", "Charity"
It isn't charitable to call another person a fool, but you can acknowledge that the person has made a foolish mistake (in your perception, and in view of the consequences).
I've given judgement of others some thought and various times in my life and written a number of prayers relating to that e.g
Judge you, my brother?
God, eternity waits for those who live the gospel to truly share in Your delight in each person. With You, we will rejoice in everyone who accepts Christ’s invitation to follow Him with prayer, penance and generosity!
How profound is the giving required by that person, and this! What happiness, what anguish is known there! What temptation is encountered! What sensitivities enfeeble or enrich and sanctify that life! How great is Your glory in the strange or ordinary facts and struggles of their existence! Yet, how can we know?
We err in applying rules of private interpretation to another’s intention or act, except as feeble measure for our compassion and charity. Only by one’s private consciousness—unless enlightened by Your Spirit of love—can each see what lies in another’s soul.
Each person is a unique expression of Your love, an individual world, some great, and some miniature, separate in existence and consciousness, yet united in You. Yet how quickly do we judge each other! We offer You our hurt and theirs in prayer for healing and forgiveness.
Let us not belittle or betray, in thought, or by gossip—the seemingly sinful, the apparently misled or foolish, [FONT=Book Antiqua]or those perceived to be ugly, or crippled in mind or spirit. Let us celebrate their preciousness in You. Let us no longer sin against Your sacred love and creation in anyone by our judgements however seemingly justified. [/FONT]
Let Your Holy Spirit know and love each other person through us, with sensitivity to their emerging needs. Give us compassion for each other, however perplexed or inaccurate our perception, so that we revere each other—and ourselves—as individuals sacred to You.
Through Your Spirit, we can offer appreciation, justice and love to each other as we wait humbly on the full vision of Your meaning, purpose, and love of each person, in the final translation that follows death. Let us [FONT=Times New Roman]serve and intercede for each other person as loved child of God, in glad, trusting welcome.[/FONT]