How would Joseph and Mary bring fruitful and multiplying be of any harm to their integrity? They were not forbade further children by Jesus or the angels.
It is the fundamental mark of her consecration to God. It is fitting for her dignity and integrity.
https://stpaulcenter.com/understanding-marys-perpetual-virginity/
Discussion
The most Holy people throughout the scriptures were celibate. Christ sets the highest standard & example for us to follow.
Paul goes on to encourage a monastic, ascetic lifestyle if possible (not possible for most, in which case he says to get married so you don’t fall under sexual temptation/sin).
That way, you can fully focus on following and becoming more like Christ.
Keeping this in mind, check out this video which summarizes the view that the Church has always had of Mary - that she was the Mother of God (Theotokos), the very first Christian, and that she is the most Holy woman to ever live:
Good points! Mary was a temple virgin in the customs of the Jews of the time. More about that here:
https://taylormarshall.com/2011/12/did-jewish-temple-virgins-exist-and-was.html
They were not forbidden from having children. They choose this of their own free will.