Irenicist:
In the same way as the baptised infant is brought into the Church while in a state of invincible ignorance, so too can adults.
Only adults that suffer from some form of arrested brain development can be assumed to possess an invincible ignorance that cannot be overcome by proper catechesis. All other adults are assumed to be able to receive the instruction that they need to make the Profession of Faith.
The Church used to be clear about what was expected from adult converts:
The Roman Ritual
Reception of Converts
Profession of Faith (short form, pp. 35.)
I., N. N., having before me the holy Gospels, which I touch with my hand and knowing that no one can be saved without that faith which the Holy, Catholic, Apostolic Roman Church holds, believes, and teaches, against which I grieve that I have greatly erred, inasmuch as I have held and believed doctrines opposed to her teaching –
I now, with sorrow and contrition for my past errors, profess that I believe the Holy, Catholic, Apostolic Roman Church to be the only and true Church established on earth by Jesus Christ, to which I submit myself with my whole soul. I believe all the articles of Faith that she proposes to my belief, and I reject and condemn all that she rejects and condemns, and I am ready to observe all that she commands me. And I make the following profession of Faith:
I believe in only one God in three divine Persons, distinct from, and equal to, each other – that is to say, the Father, the Son, and the Holy Ghost.
I believe in the Catholic doctrine of the Incarnation, Passion, Death, and Resurrection of our Lord Jesus Christ; and the personal union of the two Natures, the divine and the human; the divine Maternity of the most holy Mary, together with her most spotless Virginity.
I believe in the true, real and substantial presence of the Body and Blood, together with the Soul and Divinity, of our Lord Jesus Christ, in the most holy Sacrament of the Eucharist.
I believe in the seven Sacraments instituted by Jesus Christ for the salvation of mankind – that is to say, Baptism, Confirmation, Eucharist, Penance, Extreme Unction, Order, Matrimony.
I believe in Purgatory, the Resurrection of the Dead, Everlasting Life.
I believe in the Primacy, not only of honor, but of jurisdiction, of the Roman Pontiff successor of St. Peter, Prince of the Apostles, Vicar of Jesus Christ.
I believe in the veneration of Saints and of their images.
I believe in the authority of the Apostolic and Ecclesial Traditions, and of the Holy Scriptures, which we must interpret and understand only in the sense which our holy mother the Catholic Church has held and does hold.
And I believe in everything else that has been defined and declared by the sacred Canons and by the General Councils, and particularly by the holy Council of Trent, and delivered, defined, and declared by the General Council of the Vatican, especially concerning the Primacy of the Roman Pontiff, and his infallible teaching authority.
With sincere heart, therefore, and with unfeigned faith, I detest and abjure every error, heresy, and sect opposed to the said holy, Catholic and Apostolic Roman Church. So help me God, and these His holy Gospels, which I touch with my hand.