You make a great point about culture existing at different levels.

For example, in my household, we have a culture of not wearing shoes indoors. However, this isn't because we're "shoephobic"; rather, we've found that it keeps our home cleaner. Guests can wear shoes in their own homes, but when they visit us, we kindly ask them to follow our house rule. My wife would understandably be annoyed if I disregarded this rule and allowed guests to traipse through the house in shoes. Our household culture has developed logically over time based on practical experience. On the other hand, if we had a rule like "no pink socks" without any logical reason, it would seem arbitrary and unwelcoming.

On a larger scale, whilst we have nation staters (for good or bad), and because this is the level where immigration is controlled, it seems of relevance to try and define a culture at that level. Nation-states have their own cultures, often shaped by centuries of experience - slowly adapting over time. In the UK, for example, our culture includes following English law, which has (generally) served us well over time. For example, a significant part of this culture is that citizens do not openly carry firearms, and many would be angry to find out if border control had allowed large numbers of gun-totting Texans in with firearms. We have no issues with Texans open carrying if that's what they choose to do in Texas. However, it wouldn't be fair to exclude Texans based on say, wearing cowboy hats.

(You know I always value your opinion Ben, all love here xxx)