What does this quotation exactly mean?

I think he means that in the USA the consequences for criticizing the USA are too harsh and disproportionate for what was said. It is objecting to the way that patriotism overrides discussion and honest appraisals of situations. He is saying that, even if the US does something that causes them to be disliked or retaliated against it is not the fault of the US but has to be due to some problem with others, because the USA is inherently good. To say that the USA is not loved is to imply that they are doing harm or something wrong which brands you as a 'traitor'.

This theory says that artists are useful to society because they are so sensitive. They are super-sensitive. They keel over like canaries in poison coal mines long before more robust types realize that there is any danger whatsoever.