Actually, it’s very important to divine justice that everybody hear what everybody has done, good and bad, and that everybody witness the justice and mercy of God, in the light of knowing the truth about everybody’s deeds. Doing things openly and publicly has been part of jurisprudence since the earliest times, and it is enshrined in common law. It’s why the elders of Jewish cities sat in the city gates to give judgment, and why the king gave judgment in his public throne room, in front of all onlookers. The ancients would have known what to think about judicial abuses and strange decisions, like sealing records away from the people or holding secret trials.
In any case, everyone in Heaven does know, and every saved person will “know fully, even as I am known” by God. (1 Cor. 13:12) That’s the beatific knowledge, which includes all sorts of things, from explanations of the full workings of Creation and Nature to the lives of your fellow members of the Body of Christ.
So really, when you think about it, the general judgment is for the benefit of those people who are damned, so that they will know that they had as fair a chance as anybody.
By knowing the full facts about everything that has ever happened, we will also know why God has allowed certain overwhelmingly bad or good things to happen to people, especially when they do not know why they happened and do not seem to deserve them. The general judgment will allow both good and bad people, and good and bad angels, to judge God’s actions according to His own account, so that we will know for certain that He is good and worthy of praise, and we will give Him glory.
St. Augustine talks about this at length in Book 20 of The City of God. Here’s a comment from the end of Book 20, Chapter 1:
“… the last judgment, when Christ is to come from heaven to judge the living and the dead. For that day is properly called the day of judgment, because in it there shall be no room left for the ignorant questioning why this wicked person is happy and that righteous man unhappy. In that day true and full happiness shall be the lot of none but the good, while deserved and supreme misery shall be the portion of the wicked, and of them only.”
He adds in Chapter 2:
“… when we shall have come to that judgment… we shall then recognize the justice of all God’s judgments: not only of such as shall then be pronounced, but of all which have taken effect from the beginning, or may take effect before that time.”
The Roman Catechism of the Council of Trent (the old old catechism that was replaced by the Catechism of the Catholic Church, and which was for the use of priests as a guide for teaching their congregations) backs this up in Article VII: “He Shall Come to Judge the Living and the Dead.”
“… when on the same day and in the same place, all men shall stand together before the tribunal of their Judge, that in the presence and hearing of all human beings of all times each may know his final doom and sentence. The announcement of this judgment will constitute no small part of the pain and punishment of the wicked; whereas the good and just will derive great reward and consolation from the fact that it will then appear what each one was in life. This is called the general judgment.”
[Several arguments follow for why God would hold a general judgment. You’ll have to see if these arguments would help your friend; they are provided for pastoral purposes.]
"Finally, it was important to prove, that in prosperity and adversity, which are sometimes the promiscuous lot of the good and of the bad, everything is ordered by an all-wise, all-just, and all-ruling Providence: it was, therefore, necessary not only that rewards and punishments should await us in the next life, but that they should be awarded by a public and general judgment.
“Thus they will become better known and will be rendered more conspicuous to all; and in atonement for the unwarranted murmurings, to which on seeing the wicked abound in wealth and flourish in honours, even the Saints themselves, as men, have sometimes given expression, a tribute of praise will be offered by all to the justice and Providence of God. ‘My feet,’ says the Prophet [David], 'were almost moved, my steps had well nigh slipped, because I had a zeal on occasion of the wicked, seeing the prosperity of sinners;” (Ps. 73:2) and a little after: ‘Behold! these are sinners and yet abounding in the world, they have obtained riches; and I said, Then have I in vain justified my heart, and washed my hands among the innocent; and I have been scourged all the day, and my chastisement hath been in the morning.’ (Ps. 73:12-14) This has been the frequent complaint of many, and a general judgment is therefore necessary, lest perhaps men may be tempted to say that ‘God walketh about the poles of heaven, and regards not the earth.’ (cf. Job. 22:14)
“Wisely, therefore, has this truth been made one of the twelve Articles of the Christian Creed, so that should any begin to waver in mind concerning the Providence and justice of God they might be reassured by this doctrine.”
I’ll look and see what else I can find for you.