First, it is not the case that the early Fathers of the Church were anything at all like modern Protestants in their derisive attitude toward the Blessed Virgin. On the contrary, they greatly extolled her purity and virtue as being beyond compare. The only question that remained in their mind before the Church had spoken was whether the Immaculate Virgin was free merely from actual sin or even from original sin itself.
In fact, the early Fathers, apart from their many other praises, almost unanimously called her the New Eve as Christ is called the New Adam. And the dogma of the Immaculate Conception is contained in this, though not all drew that inference immediately. For they agreed that Mary in her purity was preserved inviolate to bear Christ like the Ark of the Covenant and in a state loftier than Eve had been before her fall. But Adam and Eve alone were created without original sin, in the state of sanctifying grace. Therefore, from this it follows that Mary, the New Eve, too was created without original sin.
It should go without saying that attempting to quote St.Thomas against the authority of the Roman Catholic Church is so absurd it cannot hope to stand. Read the quote in my signature, to see how in his humility the Angelic Doctor's attitude towards the Church of Peter should be a model to all who hope to study theology, especially given his universally admitted towering intellect.
Gobosox, if you are sincere, here's a suggestion - it is not through knowing the true doctrine on all possible questions that we seek among a multitude of sects to find the true Church, but through knowing by plain sight and the easiest of means the true Church that all men, learned and simple alike, can know with solid certainty and with no trace of error the true doctrine of Christ.
This is Christ's own means of settling all disputes among those who claim to be His followers. Simply tell it to the Church - and listen to Her voice which forever settles the question (Mat 18:17). For this reason, St.Paul calls the Church, not the Scripture, "the pillar and foundation of the truth" (1 Tim 3:15).
Instead, ask yourself where and where alone the true Church can be found and with what marks she can be known, since the time of the Apostles. These are Apostolicity and Catholicity.
To the early Christians, there was only one answer. To avoid all possible heresy, go to that Church which alone has and can demonstrate succession from the Apostles in her Bishops from the earliest times, and this all around the world, wherever the Apostles went, and most especially in the Roman Church which, with docuмented historical evidence, from St.Peter through St.Linus, St.Cletus and St.Clement, the first four Bishops of Rome through their successors there in the present day.
She is the one, true Church of Christ, and if impious men like Luther who seems to have influenced you called her AntiChrist, that was only because he was possessed with the same spirit of the Pharisees, who saw God Incarnate and called Him Beelzebul. As He Himself said, the same must necessarily happen of his true Church as well, that misguided men say the same of her. (Mat 10:25)