There is none. You're simply rendering an opinion. Are you too blind to see that? You know what goes on in this man's heart? You know even less about about Catholic doctrine.
A reasonable objection to the teaching on Mary being a perpetual virgin.
In the Greek, Luke uses the phrase τὸν υἱὸν αὐτῆς τὸν πρωτότοκον, translated literally as the son of her, the firstborn. In English we would say, her firstborn son.
The key word in this section is πρωτότοκον (prototokos). It means first, pre-eminent; the first among others. It allows for other children to be born to Mary.
Contrast this with John 3:16 where John uses the Greek Υἱὸν τὸν μονογενῆ, literally Son the only begotten.
The key word is μονογενῆ (monogenes). It means one and only; one of a class.
We know this is the correct description of Jesus as He is the only Son of God.
However, He is not the only son of Mary. Recall that Luke was a physician who by his own account researched a lot so we would have an accurate account of what happened.
If Luke wanted to indicate Mary had only one child he would have used the phrase John did.
In reading the accounts where the brothers and sisters of Jesus are mentioned we need to keep the verses in context.
We have the account of Paul in Galatians where he noted he met James, the Lord's brother among others.
These are not cousins of Jesus as the word cousin, ἀνεψιός, is used only in reference to Barnabas's cousin Mark. As Paul had traveled with Barnabas so he would know if he was a cousin or a brother or other relative.
The key to all of this is allowing the Word to interpret the Word. Understanding the Greek also helps.
Who interpreted it for the writers? And without infallibility somewhere along the line, it's a pretty flimsy foundation, isn't it?
It might help to know Greek. But it's hardly a requirement for knowing the true faith.
The capacity to learn, as with the Greek, is a gift from God and ought not to be lorded (no pun intended) over others, not taken for granted. I rely on the Teaching authority, the Magisterium of the Church for interpretation. I am not too proud to admit if i don't know something, and many holier people, more scholarly people, and better human beings than I have done the interpretation for me. I have the advantage of the fruits of their labor.
It is worth noting that the Jews did not rely solely on the Torah, but on oral tradition as well during the time of the Second Temple, during which Jesus lived.
...Nevertheless, Jews sought to determine from the Torah all of the details of a complete legal system. As tradition describes it, from the time of the very giving of the written Torah, Moses already had received a companion Torah she'b'al peh (oral Torah), which he proceeded to teach to the people of Israel during their travels in the desert. It is clear that from the very beginning, Jews needed additional authoritative law, or halakhah ("going," or "path"), to govern regular life. These halakhot (plural) were passed on through the generations, and during the period of the Second Temple (fifth century BCE-first century C.E.), halakhot, both those developed through custom and those derived from interpretation of the Torah, were collected and transmitted. Following the destruction of the Temple in 70 C.E., the earliest rabbis gathered and transmitted the laws learned from earlier sages.
...Everywhere and throughout the Talmud, the rabbis worked with several basic assumptions. Given a controversy between two early sages, the goal was not to determine according to whom was the practical law; the goals was to make sense of each opinion. This underlying assumption that opinions are not simply fickle choices but the rational decisions of sages confronting differing ways of describing legal reality, is the hallmark of the Talmudic process.
Also worthy of note is that the Rabbis were the one considered the wisest, most learned, and holiest- NOT ORDINARY MEN. By the time the oral tradition was written, one of these was the great Gamaliel, personal mentor of Saul of Tarsus- later to become St. Paul.
Thus, in their practice of Judaism, neither Jesus Himself nor St. Paul were instructed only through the written Torah, but Jewish Sacred Tradition, as well. Not sola scriptura.