Part of the joy in interacting with people from other parts of the world is to grow in an appreciation and understanding of varied personalities, customs, and yes, opinions. Sometimes in our differences we can see how much the same we all are in purpose.
Perhaps because I am an American, I more often notice that it seems to be other Americans who want to deny their nationality and advise others to do the same. Do what you want, but I find that advice to others misguided. That’s not to suggest marching down the street chanting USA, USA. Rather, when traveling instead of hiding our identity, we can become ambassadors of a sort for our county. Act respectfully. If we all do so it is doubtful that we or our country in general will be met with negative sentiment.
I lived many years in Europe and continue to travel extensively both for business and pleasure to virtually all parts of the world. I am a proud American. No reason to hide it, no reason to apologize.
As for people with flags and other identifiers on backpacks, I rather enjoy knowing where a person is from. It is often a conversation starter.