What I understand about how this doctrine came about does not impress me as trustworthy. Visions, miracles, etc. are claimed by many false prophets. There might be something to them, but it does not necessarily follow that it is by God.
The virgin birth and immaculate conception of Jesus is perfectly biblical gospel. Going further than that is unnecessary and unbiblical. The simple Gospel is sufficient without adding “new light”. I simply do not trust additions to the faith once delivered.
Luke 1
26 In the sixth month, the angel Gabriel was sent from God to a town of Galilee called Nazareth,
27 to a virgin betrothed to a man named Joseph, of the house of David, and the virgin’s name was Mary.
28 And coming to her, he said, “Hail, favored one! The Lord is with you.”
In calling her the “favored one” the angel Gabriel is saying that Mary was set aside for a special purpose. She was to be the mother of the Son of the Most Holy through the Holy Spirit. Now for the logic, if Jesus was fully God AND fully man and would have inherited attributes of both his parents, then he would have inherited from Mary. If Mary were subject to original sin, it would make sense that Jesus would have been subject to original sin and we can’t have that. So, in order for Mary to be the Holy vessel to carry Gods Son, it would make sense that God would have wanted her to be made as pure as possible. I can’t see God sending His Son to a dirty vessel. To make her pure enough to carry the Son of God, she had to be created without original sin, hense comes the first definition of Immaculate Conception.
Some reading suggestions that go back to at least the 2nd century AD
The Fathers call Mary the tabernacle exempt from defilement and corruption (Hippolytus, “Ontt. in illud, Dominus pascit me”);
Origen calls her worthy of God, immaculate of the immaculate, most complete sanctity, perfect justice, neither deceived by the persuasion of the serpent, nor infected with his poisonous breathings (“Hom. i in diversa”);
Ambrose says she is incorrupt, a virgin immune through grace from every stain of sin ("Sermo xxii in Ps. cxviii);
Maximus of Turin calls her a dwelling fit for Christ, not because of her habit of body, but because of original grace (“Nom. viii de Natali Domini”);
Theodotus of Ancyra terms her a virgin innocent, without spot, void of culpability, holy in body and in soul, a lily springing among thorns, untaught the ills of Eve, nor was there any communion in her of light with darkness, and, when not yet born, she was consecrated to God (“Orat. in S. Dei Genitr.”).
In refuting Pelagius St. Augustine declares that all the just have truly known of sin “except the Holy Virgin Mary, of whom, for the honour of the Lord, I will have no question whatever where sin is concerned” (On Nature and Grace 36).
Mary was pledged to Christ (Peter Chrysologus, “Sermo cxl de Annunt. B.M.V.”);
it is evident and notorious that she was pure from eternity, exempt from every defect (Typicon S. Sabae);
she was formed without any stain (St. Proclus, “Laudatio in S. Dei Gen. ort.”, I, 3);
she was created in a condition more sublime and glorious than all other natures (Theodorus of Jerusalem in Mansi, XII, 1140);
when the Virgin Mother of God was to be born of Anne, nature did not dare to anticipate the germ of grace, but remained devoid of fruit (John Damascene, “Hom. i in B. V. Nativ.”, ii).
The Syrian Fathers never tire of extolling the sinlessness of Mary. St. Ephraem considers no terms of eulogy too high to describe the excellence of Mary’s grace and sanctity: “Most holy Lady, Mother of God, alone most pure in soul and body, alone exceeding all perfection of purity …, alone made in thy entirety the home of all the graces of the Most Holy Spirit, and hence exceeding beyond all compare even the angelic virtues in purity and sanctity of soul and body . . . . my Lady most holy, all-pure, all-immaculate, all-stainless, all-undefiled, all-incorrupt, all-inviolate spotless robe of Him Who clothes Himself with light as with a garment . . . flower unfading, purple woven by God, alone most immaculate” (“Precationes ad Deiparam” in Opp. Graec. Lat., III, 524-37).
To St. Ephraem she was as innocent as Eve before her fall, a virgin most estranged from every stain of sin, more holy than the Seraphim, the sealed fountain of the Holy Ghost, the pure seed of God, ever in body and in mind intact and immaculate (“Carmina Nisibena”).
Jacob of Sarug says that “the very fact that God has elected her proves that none was ever holier than Mary; if any stain had disfigured her soul, if any other virgin had been purer and holier, God would have selected her and rejected Mary”. It seems, however, that Jacob of Sarug, if he had any clear idea of the doctrine of sin, held that Mary was perfectly pure from original sin (“the sentence against Adam and Eve”) at the Annunciation.
Even Martin Luther believed in the lack of original sin in Mary and her immaculate conception. The idea that it is untrue is a relatively new idea.
Enjoy and have fun.