I’ve refrained from commenting on this topic so far, as I really did not feel qualified to comment.
However, the article linked here is very interesting. Especially as it actually gives an example of an irregular marriage situation, that might not actually rise to the level of mortal sin.
Example: One who was baptized Catholic but raised without knowledge of that fact, is (incredibly) bound by canonical form and thus, if married outside of form, he or she would be, by definition, living in an irregular union. It would be ludicrous to refer to such a person as “living in sin”. I can offer a dozen more fact patterns that would duplicate this point.
I suppose one can wave this example away as irrelevant, since someone like that wouldn’t even be coming to Mass and wanting Communion in the first place.
But, I have read topics on CAF by people who have indeed found out that they were baptized Catholic as an infant, and never knew. I recall at least one post by someone who wanted to join the Church, went through RCIA, and suddenly found out that they didn’t need to go through the whole process, because they had been baptized in the Church already. What if such a person had married civilly, “joined” the Church still ignorant of their Catholic baptism, and gone to Communion? Since from what I understand, the Church does NOT require that converts from other faiths have their marriages, even civil ones, be convalidated if they convert. They are considered valid.
Certainly, some parents have babies baptized in the Church under social pressure, to please relatives, etc, but never planned to raise them Catholic in the first place. Or, they may convert to another branch of Christianity and stop considering themselves Catholic.
I’ve also read of well-intentioned grandparents or other relatives who take it upon themselves to secretly baptize babies if their own parents refuse to have them baptized Catholic. If such people never actually admit that, though, the child may grow up ignorant of that.
I can also think of a situation akin to “Martin Guerre”, assuming the wife really was fooled into thinking her real husband had returned (I know this is dubious but we’ll never know), she would have been objectively guilty of adultery, but not been “living in sin”, and AFAIK, her children with the imposter were actually “legitimized”.
Or, situations where a spouse is presumed lost at sea, killed in action in a war, etc. I actually know of a case happening in WWII to a distant relative of mine. He was presumed killed in action, and his wife remarried. But he’d actually been taken prisoner. When he returned, his wife did not wish to leave her new husband, I believe because they had children by that time. My relative actually died not long after from effects of his imprisonment, and the situation resolved itself.
And while I’ve noticed that most of the commentary posted on CAF about this comes from the US, or Europe, I can certainly think of many “developing” countries, often affected by civil wars, in which spouses might indeed go missing and be presumed dead, when they’re not. I guess some spouses would wait indefinitely, I can imagine some posters here who would state that if they don’t, they are sinning… But if they were actually given an official notice of death, are they really in a “state of mortal sin”?
Also, in many such countries, a woman simply cannot support herself without a man. Remarrying would be a matter of survival. Indeed, I believe that is why Christ stated that a man who divorces his wife “causes her to commit adultery”, because that was indeed the case for most women back in Biblical times, that a woman who is divorced would starve if she didn’t remarry or become a prostitute. Again, I suppose the saintly thing to do is for a wife to still refuse to remarry, even if it means starving to death. But I suspect that if she DOES remarry, her culpability is greatly reduced.