Intermarriage has always been a problem, all the way back to Romeo and Juliet (and West Side Story, of course). Intermarriage de-demonizes the ‘other’, and the insecure tribe member sees this as an existential threat, the beginning of the end of tribal cohesion.
Gangs in LA view high school as a threat. A kid who graduates from high school has options, can see a way up, which decreases the power of the gang and its leaders. Public school is seen as a threat by some tribes, a secular indoctrination and an exposure to other cultures and points of view that might destabilize what has been built over generations. And digital audio is a threat to those in the vinyl tribe, because at some point, some members may decide they’ve had enough of the old school.
Lately, two significant threats seen by some tribes are the scientific method and the power of a government (secular, or worse, representing a majority tribe). One fear is that once someone understands the power of inquiry, theory, testing and informed criticism, they will be unwilling to embrace traditional top-down mythology. The other is that increased government power will enforce standards and rituals that undermine the otherness that makes each tribe distinct.
If a tribe requires its members to utter loyalty oaths to be welcomed [“the president is always right, carbon pollution is a myth, no ____ allowed (take your pick)”] they will bump into reality more and more often. I had a music teacher in elementary school who forbade students to listen to pop music, using a valiant but doomed-to-fail tactic of raising classical music lovers.
Tribes started as self-defending groups of wanderers. It didn't take long, though, for them to claim a special truth, for them to insulate themselves from an ever-changing world.
In a modern, connected era, successful tribes can’t thrive for long by cutting themselves off from the engines that drive our culture and economy. What they can do is engage with and attract members who aren’t there because the tribe is right and everyone else is wrong, but instead, the modern tribe quite simply says, “you are welcome here, we like you, people like us are part of a thing like this, we'll watch your back.” It turns out that this is enough.