Do not feel bad Cromlech. This is a sign of the times. Anti-patriotism is cool right now. A similar crowd in New York, L.A., Paris, Berlin, or Tokyo, might just as well have boo'd "G-d save the Queen" for exactly the same reaons.
When our band pipes up "G-d save the Queen" I stand up. I remove my hat. I place my hand on my heart. Not because I particularly think that the British monarchy is the greatest thing ever, not that I think your current monarch is the greatest thing ever (although, everything I've read about her indicates to me that she's a top notch human being), but because I respect people like you, Cromlech, who love your country.
I think your country is easily one of the top two or three best empires the world has ever had. My display is respect for the citizens like you who love their country.
Now, that brings me to other countries... if I go to a ballgame featuring a Cuban team, I will wait until after the niceties have been conducted to enter. Unless I am at a rally that is endosing the removal of Castro, I will not rise, I will not remove my hat, and I will not place my hand over my heart, to respect Cuba. I will go out of my way to avoid being in a place where doing so is required by good manners... even though I have no love for (the current admistration) of Cuba, like North Korea, and Iran, I love Cuba's people. I will not disrespect them by offending their national anthem if I can avoid doing so.