On Reddit, America doesn't just receive the "slightest amount of nationality based criticism." It's receives criticism for anything and everything, even when it's nothing. So it gets a little old and you're naturally going to have some that come to the defense. I actually think Americans criticize their own country more than the average citizen of the world, especially on Reddit. You see it all the time.
That being said, the USWNT absolutely deserves criticism for the over the top celebrations after the first 4 or 5 goals. I actually went back and watched to see if the criticism was warranted or if people were just piling on. It was warranted.