Doctrine in a Christian church requires a scriptural foundation. Individual beliefs not necessarily found in scripture but not in contradiction of it or forbidden by it are acceptable but are not to form the basis of doctrine. As an example, look to the typical treatment of the Apocrypha by the authorized King James Bible as well as quite a number of early, notable Christian figures. Good for edification but not for doctrine. Not forbidden, but they do not rise to the level of inspired scripture, in other words.
A thoughtful reply, to which i would say that the bible has within it everything that a Christian must believe (obviously) does not mean it must be explicitly taught, as the sufficiency of Scripture in SS refer to both the material and formal sense.
In the latter, the gospel of salvation is so sufficiently clear that a soul may, by God's grace, read a text such as Acts 10:36-47 and born again and be baptized, while also materially providing for such things as reason and for discernment of both men and writings as being of God, and thus for a canon.
But teaching as doctrines things beyond Scriptural testimony is itself contrary to Scripture, thus we are "not to think of men above that which is written," (1Cor. 4:6) and which certainly applies to Mary.
However, the weight of Scriptural warrant is not the basis for the veracity or RC teaching, nor it is even necessary, only that it does not contradict Scripture. Yet which is autocratically determined by Rome based upon her premise of assured veracity as the claimed historical instrument and steward of Divine revelation, which itself is not Scriptural.
For Rome has presumed to infallibly declare she is and will be perpetually infallible whenever she speaks in accordance with her infallibly defined (scope and subject-based) formula, which renders her declaration that she is infallible, to be infallible, as well as all else she accordingly declares.
And as no less an authority as Manning asserted,
It was the charge of the Reformers that the Catholic doctrines were not primitive, and their pretension was to revert to antiquity. But the appeal to antiquity is both a treason and a heresy. It is a treason because it rejects the Divine voice of the Church at this hour, and a heresy because it denies that voice to be Divine...I may say in strict truth that the Church has no antiquity. It rests upon its own supernatural and perpetual consciousness....The only Divine evidence to us of what was primitive is the witness and voice of the Church at this hour.. — Most Rev. Dr. Henry Edward Cardinal Manning, Lord Archbishop of Westminster, “The Temporal Mission of the Holy Ghost: Or Reason and Revelation,” (New York: J.P. Kenedy & Sons, originally written 1865, reprinted with no date), pp. 227 .
Thus faithful RCs are not to objectively examine evidences in order to ascertain the veracity of official RC teaching, as "He is as sure of a truth when declared by the Catholic Church as he would be if he saw Jesus Christ standing before him and heard Him declaring it with His Own Divine lips." (Henry G. Graham, "What Faith Really Means")
"in all cases the immediate motive in the mind of a Catholic for his reception of them is, not that they are proved to him by Reason or by History, but because Revelation has declared them by means of that high ecclesiastical Magisterium which is their legitimate exponent." — John Henry Newman, “A Letter Addressed to the Duke of Norfolk on Occasion of Mr. Gladstone's Recent Expostulation.” 8. The Vatican Council lhttp://www.newmanreader.org/works/anglicans/volume2/gladstone/section8.html
But the church did not begin under the RC premise, but upon Truth claims being established upon Scriptural substantiation in word and in power. Doctrines can have both explicit texts for support, as well as the weight of Scriptural substantiation that disallow the contrary conclusion. Seeing what is both explicitly and or manifestly substantiated by Scriptural substantiation eliminates that which is not as having warrant as doctrine, while teaching what is at best only conjecture or speculation (i.e. Mary being bodily assumed) as doctrine is itself a false doctrine.
The Trinity has texts clearly calling Christ God as well as ascribing uniquely Divine attributes and glory to Him and the Spirit, which renders God being a Trinity of persons having the same nature, with an order within it, as a logical necessity.
Homosexuals will argue that nowhere are "loving, monogamous homosexual relationships condemned," and that only those which are associated with idolatry are condemned. But such a hermeneutic would also allow "loving, monogamous bestiality relationships," while disallowing the 10 commandments as well as most all others, as they usually are contrasted some place with the immorality of idolators.
Moreover, nowhere is motive a determining factor in proscriptions against illicit sexual partners. and God only sanctioned sexual unions btwn opposite genders, which the Lord Jesus also specified, (Mt. 9:4-6) that being by marriage, leaving all others as fornication. Meanwhile Scripture only condemns homosexual unions wherever they are manifestly deal with, both by precept and in principle, by design and decree, showing man and women being created uniquely compatibly and complimentary, and uniquely joined in marriage.
. Going from this, it would appear the issue is not that the Catholic Church teaches that Mary is the new Eve. . At best the issue is that the Catholic Church claims one must believe it.
That Mary was/is the New Eve, as meaning all what Rome attributes to her as the Mother of the whole Christ and the Church who continues in heaven to exercise her maternal role on behalf of the members of Christ, (CCC 975) " is not only unwarranted by Scripture but as a whole is contrary to it.
The Holy Spirit characteristically mentions exceptions to the norm among notable persons, from great age (Methuselah), to excess size, fingers (Goliath), strength (Samson), devotion (Anna), diet (John the Baptist), to the supernatural transport of Phillip, the singleness of Paul and Barnabas, and uncharacteristic duplicity of Peter, and the surpassing labor and suffering of Paul, etc., etc. to John the Baptist "being" Elijah, and Christ being sinless and the prophesied Messiah and Divine. But Mary is nowhere presented as being a sinless perpetual virgin and highest created being in virtue, titled the mother of God and bodily assumed into Heaven and crowned as its Queen, with authority over angels, and hearing virtually infinite amounts of prayer from earth addressed to her, etc.
And in contrast, Scripture teaches that God can use impure vessels to convey that which is pure, as He did with His words, and that if Mary was sinless, then her parents were not, nor Israel "of whom Christ came as concerning [like Mary] the flesh," [Rm. 9:5) a distinction Catholicism fails to make, though Catholics even stress Jesus owes His Precious Blood to her.
And instead of Mary being the greatest created being as the New Eve, as RCs assert, at the time of Mary, according to the Lord Jesus Himself John the Baptist was the greatest created being born of women, and with Paul bringing forth more spiritual children. If Mary is credited with being the mother of the church due to her instrumentality in bring forth Christ, then her parents were the grandparents, while Scripture points to Israel as being the root which enabled the Gentiles and hence the "one new man" church to be grafted in. (Rm. 11:17,24)
In addition, Scripture only teaches that the crowning of resurrected saints takes places at the Lord's return, while nowhere is anyone but pagans shown praying to anyone else in Heaven but the Lord, and that being able to hear virtually infinite amounts of prayer from earth is a uniquely Divine attribute.
To this can be added multitude other Catholic teaching which think of Mary "above that which is written," but is explicitly or implicitly sanctioned. And which rest upon arguments from silence and egregious extrapolation, which places one in the realm of cults.