Which of your identities is more fundamental to who and what you are, nationality, religion, political ideology, football team, other? What about human?
None of the above. Being human is no more a part of my identity than is being right-handed, short, or having green eyes. It's what I am and I had no say in it. My identity is composed of my relationships, my choices, and my experiences. Most fundamental... hard to say, probably centered around my career. But identity isn't a one-dimensional thing. It's composed of many elements. So actuary, spouse, daughter, sister, friend, atheist, internet-arguer, cat-owner... the list goes on and on. But "human" isn't an important part of what makes me myself. It's simply what is.
Tribalism is not only unnecessary, but detrimental to survival in this global tribe of seven billion.
Maybe. Maybe not. I'm not convinced that it's unnecessary as an entire concept. I do agree that some "tribes" are pointless. Racial tribes, for example, are really pretty dumb. But group formation - including protection of the group - is a pretty fundamental element of social animals overall. We're stronger together... to a point. Empathy is an important element of social groups, it's what allows us to bond, to feel for another, and to sacrifice our own immediate desires for the well-being of others. But without some limitations, it can very quickly overwhelm.
If you felt as much care for every person on the planet as you felt for your mother or your child or your spouse, it would quickly become impossible to make choices. Would you be willing to forego a dinner of your own in order to make sure that your child got fed? Probably. Would you be willing to forego a dinner of your own in order to make sure that a stranger in Kazakhstan got fed? How many hungry strangers are there in Kazakhstan? How many dinners are you willing to forego? Would you be willing to have your ailing parent move in with you so that you could care for them? Perhaps. Would you be willing to let an ailing stranger move in with you so that you could care for them? How many strangers are you willing to let move in? How many ailing strangers are there in your city or state?
All of us form groups. All of us are selective in the company we keep and the investment we put into other people's well being. All of us will be faced with choices about how to divide our time and our care and our energy. Most of us form multiple groups - groups are fluid and multifaceted, just as humans are. We shift between those groups, and as we do our level of commitment and our level of devotion to those groups also shift. Not all of our groups are as important to us as others. And all of us - and I do mean ALL - have people that we exclude from our groups. Sometimes for very good reason, sometimes for reasons I think are petty and irrational.
I'll happily discuss what kinds of group definitions have utility, and which kinds are idiotic. I'll happily dig in on what attachments and resonances are good and which are detrimental. But the idea that there is only one single group is tantamount to saying that there are no groups at all. It simply is not reality. It's not how humans, or any other social animal, operates.