I think they are saying that it's difficult to "maintain manners" for hundreds of thousands to millions of diverse "I, the individual" 's. It's great that you don't struggle with that yourself, but your manners can be made entirely irrelevant by 1 person in a public place who has anti-social behaviors (doesn't share the same set of "required" values for that society).
You're right, it can be read as it being difficult for society to maintain manners. I agree and I should have been clearer. But I also think you may be misunderstanding what I said to fit it into your own model. There is a difference between manners and what results from them. You can maintain (what you believe to be) good manners without it improving society to your liking. This is "irrelevant" in the sense of not changing things, but it is not irrelevant to maintaining your manners. Conforming to the bad manners is the more likely culprit to the bad outcomes anyway.
Caving on manners to avoid the "struggle", or rather, caving on manners because one benefits from doing so is just a reflection of how much one values the values. This is simply saying that more often than not we can maintain them, it just might not be worth it to us.