Family is also a common subject of small talk ("How is your wife doing?"), which is identity-plus-plus for most people, and the mating habits of snails are topics most people weakly identify with but not commonly used for small talk, so I'm guessing that relationship is a little less persuasive than it seems to be at first brush.
The real issue is whether the identities conflict. It doesn't hurt my marriage to know that your marriage is great. Meanwhile, knowing someone is a proud follower of the One True Way threatens your identity as a member of the One True-Er Way.
Though if you both happen to be members of the same True Way, starting a conversation about religion and politics can be incredibly beneficial. I know seeing a bunch of Ayn Rand books on a friend's shelf boosted our relationship immensely.
I think what he meant by "weakly identify with" was that people have opinions about these things but aren't hardcore about them. People will identify with the movies they like, what kind of pets they prefer, etc. On the other hand, I feel like very few identify with snail mating at all.
Right, but the thesis is that it is unsafe to even mention identity because it invites catastrophic conversational degradation. The observed ability to talk about family without someone saying uncharitable things about your wife cuts against the thesis.
Both participants need to identify strongly. If two guys strongly identify over the same woman there will be trouble with any talk about her. People fight over sporting teams, but you can ask a fan about the season without conflict if you don't identify with the sport.
