Mitt Romney was heckled...

...yesterday by a protester carrying a sign that said, "End Climate Silence." He was quickly drowned out by the crowd, which chanted "USA!, USA!..."

And I've noticed this before; hecklers at Republican rallies are often countered with the "USA!" chant. And I wonder: is it unpatriotic to heckle Republicans? Or is it unpatriotic to talk about climate change? Why, exactly, do these crowds always chant "USA?" What does that have to do with anything?

Do they think, somehow, that only Republicans love America?