"They are a very young couple who had one DC by accident and not surprisingly, at only 23yrs, he isn't ready to have another."
No, it isn't remotely surprising.
But it still doesn't excuse being so horrible to his wife because she assumed (entirely reasonably) that they would have more children one day.
And neither is it surprising that a young woman who has ended up married to a college boyfriend after they had an accidental pregnancy hadn't thought through how many children she might eventually want, or how their lives together would pan out.
And yet his woman has been pilloried on here by far older women, who are basically telling her that it's tough shit if she has made a mistake by marrying this man because they want different things, that now that she's married with a child she has to sacrifice the rest of her life to his whims and desires.
If he never wants any more children, and she does, then it is entirely reasonable of her to consider whether their marriage will go the distance.
Whether or not she needs to make this decision at such a young age is another matter. I tend to agree with you that 23 is too young to be tied down like that, it's not what I want for my children.
OTOH if they should find themselves married with a child at 21, I might advise them to have all their children young to give them more flexibility when they're older. The worst childrearing scenario I can personally imagine is having very spaced out children throughout your entire 20s and 30s.
So it's not necessarily the case that the best thing to do is just wait around hoping he'll change his mind. We advise women on here not to do that all the time, because when someone speaks to you, you should listen.
I think she should raise this again, calmly, and see if she can find out what his real feelings are. Then she should think about what kind of life she wants, and then talk to him again about whether their goals are as compatible as they thought when they decided to marry.
The absolutely last thing she should is decide to sacrifice herself to him and this relationship, or presume that eventually he'll change is mind. Either of those things will mean a corrosive, unpleasant relationship that will probably founder anyway.