There is still a contingent in US that thinks a person's commitment to their partner is an unbreakable bond and breaking that trust is a big deal. Lots of people will honor business deals over honoring their partner 'vows', formalized as marriage or not. Now, if both parties to a 'union' are in agreement on what is allowed, not a problem with me. Schwarzenegger having a kid with the nanny, a problem because the wife (with their 4 kids together) clearly didn't know anything about it. The 3-way neighbors (2 men 1 woman) down the street from me who are all co-habitating and raising 2 kids, well, .. everyone there is in on the decision and has full knowledge.

That's why I believe these things are still bandied about as 'consequential' in the US.