I've heard that Americans are overtly Patriotic. Why do people think there's a limit to Patriotism?

Yes i know what patriotic mean but isn't it good to be patriotic to your country? People always bash the americans as being too patriotic. I'm Canadian and I think its good that they are, there shouldn't be a limit to how patriotic a nation is. You should back it up no matter what. So could someone explain why in some peoples eyes they're TOO patriotic?