You need to seriously study Catholic theology. Point out one Church father who said Mary was sinless? You misunderstand the Immaculate Conception. Because she conceived the Son of God she was not stained with original sin.
Besides its odd isn’t it that you know better than the Church fathers, some of whom were contemporaries of John, and who infallibly sorted out the Word of God in heir interpretations of various written texts at that time when assembling together the canonical books in Scripture. Surely, if they were mistaken with Mary, then what makes you think that they were not mistaken in selecting the texts of scripture which you believe is the Word of God?
And apparently, all those pre-eminent Lutheran theologians (to say nothing of Augustine, Aquinas, Newman, and Benedict XVI -called the theological Einstein of our times) who converted to Catholicism missed your observation.
You need to seriously read the Word and quit studying catholic theology.
What do the writers of the New Testament; Paul, Peter, John, Luke, Matthew, Mark, James have in common?
Not one mentioned the immaculate conception nor did they even hint at it. Nor did they mention the "assumption" of Mary. None even hint at all of the super abilities the catholic church has bestowed upon Mary.
Just because someone is a contemporary of someone doesn't mean they cannot be without error. I note that Peter was corrected by Paul as Peter was refusing to eat with the Gentiles. We also know there was a lot of false teaching the church was battling at the time the NT was being written. That battle continues today.
Catholic apologists admit there is NO SCRIPTURAL SUPPORT for this false notion fostered by catholicism.
http://www.catholic.org/encyclopedia/view.php?id=6056
No direct or categorical and stringent proof of the dogma can be brought forward from Scripture.
http://www.catholic.org/encyclopedia/view.php?id=6056
In regard to the sinlessness of Mary the older Fathers are very cautious: some of them even seem to have been in error on this matter. (yeah, they understood she had sin so the catholic church calls them in error!)
So all the catholic can cling to on this issue is a lot of "it seems like", "it should be" and "it stands to reason". That's pretty weak justification for such a profound false doctrine.
False catholic teaching has ascribed the following to Mary: co-redemtrix, helper, advocate. Slowly but surely Mary is replacing Christ and the Holy Spirit in the catholic church.
Only Christ is our Redeemer and Advocate.
The Holy Spirit is our Helper and Advocate.
Mary, a mortal human being, cannot be involved in any of this. Yet, many in catholic church are wanting a fifth marian dogma to proclaim her as all of these and let it be official church dogma.
The whole issue revolves around who do you put your focus on and your reliance upon. Jesus or Mary? It cannot be both. If you say both, then Mary has been elevated, or more correctly, Jesus has been reduced.
Satan would love nothing more than for people to pray to Mary and rely upon Mary. Why? Because then they are not praying to or relying upon Christ. And that is, and has been, Satan's aim: to distract people away from Christ and what He does for us.