I'm not sure the Church has the authority to do that. *Maybe* she does. Perhaps one could make a case based on the Petrine Privilege. But to nullify *every marriage*? Many were certainly contracted validly and sacramentally; it seems almost sacrilegious.
Well, the Church doesn't actually nullify a marriage, it just examines them and declares them null. What they could do is assume them all to be null and require convalidation. If the are already in a valid marriage, it would have no effect. If they weren't, then they would have a valid marriage.
Typically, though, an investigation into the validity of a marriage only begins when it's clear the marriage isn't working out—when there's an obvious lack of sacramental grace. Marriages are presumed valid until proven otherwise. What you're proposing would run contrary to that entire ethos. It would implicitly impute mortal sin to, like, everybody, since living in an invalid marriage is a serious sin.
Reminds me of that priest who discovered he was baptized with the incorrect formula, and thus his baptism actually never happened. So they had to baptize him, give him all the sacraments up to Holy Orders, and then go and give all the sacraments to the people he baptized, married, etc.
They shouldn't have to redo marriages. The priest is the officiant but not the minister of the sacrament. The couple themselves administer it, having a priest present at all is merely a current discipline of the church to prevent abuse.
It's only a sin if you are aware of it, as far as I know. But you're right that it would be a big breach. On the other hand, the US has 6% of Catholics and 60% of annulments, so it's been happening in slow-motion, regardless. It just hasn't covered all marriages, but it's been massive.
It's a grave matter whether you're aware of it or not, but your degree of culpability depends on a number of things. Someone who was improperly catechized would be less culpable for entering into marriage invalidly than someone who definitely knew better. Still, if the Church were to announce that all marriages were presumed invalid and had to be convalidated, the effect is that every married person must now presume he is in a state of serious sin. Such a person would then be required to live celibately until a marriage could be contracted validly. The amount of damage that would do to the spiritual lives and consciences of the faithful would be massive.
I have often wondered why the US has more annulments. Maybe tribunals are more likely to grant them here? Maybe they are sought more often here? Maybe there are just way more invalid marriages here? Hard to tell.
Other places, Catholics only marry once in the Church, and if it is invalid nobody bothers trying to prove it because they just split up. Usually don't even file for divorce. They just leave it as a civil marriage and move on with their separate lives, until one of them dies. No remarriage wanted, no paperwork needed.
I guess it's different in the States because the civil and church ceremony can happen simultaneously, during the Mass, which conflates the two things. They're two separate ceremonies here, and the Church wedding is the higher one and that's one per customer. But even civil marriages here have a lower remarriage rate. Americans basically want to change sexual partners and get approval for each relationship, to kinda play it off, whereas everyone else is more honest with themselves that they don't have 2 husbands, they have 1 husband and 1 boyfriend. It's adultery, either way, but the second way you can at least easily dump the boyfriend and be back in good graces with the Church, or wait to marry him until after your husband dies, and you avoid the scandal of appearing at the altar dressed in white over and over and over, while you have other husbands wandering around the town. 🤪