@The Revolting Man said it well. Very few doctrinal issues are salvific, although I’ve seen and been party to many ended friendships of previously close believers due to differences of opinion over minor issues - often very minor, in my opinion.
The truth is, it’s easy to closely fellowship with likeminded believers, but that closeness can also lead to feelings of confusion, shock or even betrayal when one disagreement comes about that either or both view as very important. In fact, the closer the bond, the deeper the hurt when a disagreement occurs, and that’s true for any relationship.
I will instantly and naturally connect with other believers in plural marriage because we have that in common, but that’s just one issue (albeit an important one) of an endless array of possible and varied beliefs. And once we move past discussion on the topics we agree on, our natural desire is to discuss the many other faith related topics we’re passionate about. A common belief in plural marriage is just the tip of the iceberg and only one of
many beliefs. Moving into other topics usually leads to some more contentious debate, which is exactly why it occurs on this forum and many others.
What we need to continually remind ourselves of is the fact that no two believers will ever completely agree on every doctrinal point, and as long as they
are believers they are our brothers and sisters in Christ regardless of the disagreements we may have. That doesn’t mean we won’t desire to share our own beliefs and willingly discuss them with others who disagree, but it does mean we should prioritize our bond in Christ over some less crucial topics. Not to mention, ending relationships over debatable topics prevents either person from even sharing with or learning from the other until if and when they reconcile.
The majority of people our family is close with accept our lifestyle and can see the value of it (it’s clear to me that they do), but they don’t view it as biblically permissible and probably view it as a sin. Despite that, we choose to remain close, and I’m thankful for that. To be honest, my belief in and practice of plural marriage - although extremely important to me - probably doesn’t rank in even the top 10 of what I consider to be my most important and consequential beliefs. Likewise, several of the believers I’m closest with don’t share my belief in polygamy but do share most of my other fundamental beliefs, and I have no doubt they are true believers.