Identity and morality are way more heavily intertwined than your reasoning makes it out to be. Rules that maintain group cohesion is part of the group's identity, but you've defined that as morality. For example, the mafia is known specifically for their lack of morality within their ranks and outside of it. Religious communities have similar reputations (e.g. hating minorities, others, etc.).
My biggest objection, though, is the idea that there must be an in-group. That implies that there is an out-group. A stable society is not one where there is inequality in any appreciable amount. People in the out-group will feel like outcasts and will literally fight to become part of the in-group. I don't think anyone would call (civil?) wars a sign of stability*.
PS If you ask a less leading question you might get less downvoted
* They could be a sign of upcoming stability, though that's not the same thing.
It sounds like you've found a great guy, I can understand why you wouldn't want to let him go. I hope he sees just as much greatness in you.
Don't set yourself on fire to keep someone else warm, but if this is what you both want then give the relationship dynamic (not the fire thing) a try. I also can't help but notice that all of your examples of bad people are in the USA -- you might find a more optimistic outlook in Europe or in other developed countries.
Please don't ever believe this. It's just internalized misogyny. If you're in a relationship where you're giving more than you're getting, that's a horrible relationship and you should leave.