If you're referring to primarily on these forums, it's simply the NA vs EU argument. But where EU is a multitude of countries all taken as one entity, NA is primarily the US. So it's natural, in these debates, for the NA side to sound very patriotic and "as one" as compared to a much more diversified EU.
In real life? I'd say the US is more patriotic than average but definitely not the most. China comes to mind as a place that's definitely more patriotic than the US. But two things make the US seem worse.
1) Americans, as we all know, are a loud and brash group. Our form of patriotism is often very loud and in your face. That can make the patriotism seem like a lot.
2) There's a lot of Americans. It's a big country. The sheer volume of people voicing patriotic stances online can make it seem like we are the most patriotic people on earth.
I think there's also just a sensitivity, amongst Americans, about foreign people shitting on us. This is a country full of proud people, and a lot of us tend to get overly defensive when we feel disrespected. We're not all like that (I've never been particularly patriotic) but this is just my view from within the borders.