Your responsibility as a parent is to protect your children from that kind of behavior/conflict, Cara.
And I dont know how they were defining "harm" in those studies, but suffice to say that seperating a child from one parent (assuming both are competent parents) against their wishes is in no way helpful to them either. Moreover, conflict, grudges and sidetaking can, and often do, go on for years after a divorce. I think children could go without that too...whether the research defines that as a significant issue or not.
Lastly, I dont even think the Pope had your prior prior view of marriage. And neither do I. I belive strongly in the sanctity of marriage and preserving the family (for both religious/moral and psychological reasons) but certainly, in the case of serial adultry or violence/abuse, common sense should prevail.
I think it's a tricky question--obviously, abuse/violence is a clear and important reason (although leaving abusive relationships isn't easy, as a ton of DV/IPV research attests to), but parental dysfunction doesn't have to reach the level of "abuse" to be harmful to children either, in the long term. So, it becomes a question of whether the continual discord would be more or less harmful than the stress/issues of divorce. IIRC, research on this topic hasn't come to clear a consensus either way.
Semi-related, this reminds me of a husband-wife team of contestants on the Amazing Race about 7 years ago. The husband was screaming at his wife and telling her was going to lose it, she was sobbing, and then he shoved her backpack so hard she stumbled and almost fell down (it was definitely an aggressive shove) and then continued to scream at her. Keep in mind, he did this while he knew he was being filmed for national television. Granted, the show is designed to manufacture stress, but that was the first and only time that a contestant has ever been physically aggressive towards another contestant on camera, much less their own teammate. There was a lot of outcry at the time about how he should have been kicked off the show, should the producers have intervened to separate them and even send her to separate sequester location, could he have been arrested for assault in the country they were in, etc. To many people's surprise (and sometimes extreme distaste), they ended up staying together for several years after that and had a child before their marriage eventually ended. (Personally, I think the producers should have stepped in because, IMO, if you're violent to your wife and teammate while you know you're being filmed, I shudder to think of what you're like when you're behind closed doors.)
B) Less willing to get married
Actually, I've seen the opposite among many of my friends--people getting engaged or married after only a few months of dating. If it works for them, great, but Idk, it just seems so rushed to me...
