So what’s the big deal if Mary had more children?
Why does the thought that Mary and Joseph having a normal marriage that included sex and children throw Catholics into such a tail spin?
Because sex is EEEEEEEEEVIL.
...that and if Catholicism is ever wrong about any one thing, it opens the door to them being wrong about lots of things, and if it’s wrong about lots of things, it could be wrong about salvation, and that means that the money they spent on their scapulars was wasted.
Among other things.
Links in a chain...