That's one of the saddest things I've read, that displaying your own flag is looked down upon. I cannot imagine any long-term good coming from that kind of attitude.
For many Europeans the American attitude towards the country and the flag looks a bit like a fetish. It's a piece of the Earth within a man-made line on a map, a piece of fabric designed by some guys. The important things are of course what this symbols stand for, freedom, the American dream, going to the Moon, helping to end World War II. But then again this is also only half of the truth or do you also think of slavery, racism or the millions of victims in US (supported) wars when you look at an US flag?
Similarly the obsession with the constitution looks a bit strange from here. »I can have guns, it's good to have guns, it's in the constitution!« It is just a piece of paper, a set of laws. Some guys thought that those would make good rules to run a society and so they wrote them down. But maybe they were wrong in some regards, a constitution is no eternal God-given truth.
It really makes a difference where you grow up and to what ideas you are exposed. For the better or the worse.
Here in the USA we seldom wave state flags or chant the names of states. Maybe in Texas I could see that happening. I do recommend being the Texas of Europe.
That tends to be the opposite goal of those nationalistic flag-wavers.