Can Heaven be a reasonable alternative to Limbo for unbaptized infants?
The traditional alternatives have been Hell or Limbo, never Hell or Heaven. The Second Council of Lyon (1274) and the Council of Florence (1348) declared "that the souls of those who die in actual mortal sin or in original sin only go straight down into hell, though they will be punished differently." Pope Pius VI at the Synod of Pistoia (1526) affirmed Limbo by condemning the proposition the Pistoian Jansenists that it was just a myth, these infants went to Hell and suffered according to them. The Council of Trent (1545-1563) affirmed that men are born with Original Sin and are in need Baptism in order to be saved as follows: "If any one denies, that infants, newly born from their mothers' wombs, even though they be sprung from baptized parents, are to be baptized; or says that they are baptized indeed for the remission of sins, but that they derive nothing of original sin from Adam, which has need of being expiated by the laver of regeneration for the obtaining life everlasting,--whence it follows as a consequence, that in them the form of baptism, for the remission of sins, is understood to be not true, but false, --let him be anathema." The Church Fathers and Doctors of the Church such as St. Gregory Nazianzus (329-389), St. Augustine of Hippo (354-430) and St. Thomas Aquinas (1225-1274) have rejected the notion that the unbaptized have the vision of God. Any new doctrine has to be based on scripture, tradition or both. The notion of Heaven for all unbaptized children lacks this foundation.
The assumption that all unbaptized children go to Heaven rests on the universal will of God that all men be saved, "God our savior ... wills everyone to be saved and come to the knowledge of the truth." (1Tm 2:4) Yet God's salvific will from the beginning was conditional on man's willingness to do God's will. So, there are some intervening causes and human failures which work against man's salvation and "Lack of Baptism" cannot be excluded as a cause. Did not Christ say that unless man was reborn of water and Spirit who would not enter the kingdom of Heaven? (Robert T. Miller, Oct. 17, 2006 article in First Things)
In the Catechism Christ love for children is given as a reason for hope in their salvation. No doubt, Christ loves all children as their Creator. However, in these children there was real reason for hope because they were children of God's Promise made to the Jews. Circumcision gave them a right to rest in "Abraham's Bosom" (Limbo of the Fathers) and to be raised to the glory of Heaven with Christ's Resurrection and descent into "Hell".
Lastly, man was made for happiness and his heart is restless till it rests in God. Does Limbo satisfy man's desire for enduring happiness? St. Thomas Aquinas asserts that in Limbo there is natural happiness. Some objected that they could not be happy knowing that they had lost the Beatific Vision. St. Thomas states: "[These] children were never adapted to possess eternal life, since neither was this due to them by virtue of their natural principles, for it surpasses the entire faculty of nature, nor could they perform acts of their own whereby to obtain so great a good. Hence they will nowise grieve for being deprived of the divine vision; nay, rather will they rejoice for that they will have a large share of Gods goodness and their own natural perfections." (Summa: Supplement Appendix I, Q.1, Art 2)
St. Thomas was also asked if the bodies of those in Limbo were impassable, or free from suffering after the Resurrection. He states that there would be no suffering for them, not because they are unable in themselves to suffer, but because after the Resurrection no body is able to act upon another to bring about suffering. This is different than the impassability of the saints in heaven who do not suffer because they lack the capacity to suffer. (Summa: Supplement Appendix I, Q.1, Art 1, Reply to objection 5)
Ludwig Ott in Fundamentals of Catholic Dogma (1955) states it thus: "Souls who depart this life in the state of original sin are excluded from the Beatific Vision of God. (De fide) He maintained this as an article of faith on the based on Conciliar statements and the words of Christ expressing the need for baptism.
So, it would appear that "exclusion from the Beatific Vision" is a dogma of faith but Limbo as a place and state described by the theologians is not. Limbo is not a bad idea but a good one because "The Catholic understanding of limbo, far from being unmerciful, is a reasonable attempt to explain how infants (who are guilty of Original Sin but not of Actual sins) may be saved the pains of hell, thus attending to God's Mercy, while not violating God's own decrees of Justice regarding those (all of us) who have fallen in the Original sin of Adam. It is nowhere in contradiction to any Scriptural teaching. It is completely in accordance with God's Mercy and Justice, without giving too much weight to one or the other (since in God they are one and perfectly balanced." (The News Media Confusion About Limbo by Aristotle, a blogger)