I think that the author has a point about the underlying tone among many (not all) soccer enthusiasts that America is somehow inferior because the whole world loves soccer except us. I have found it odd that so many conservatives who like soccer will resort to 'the rest of the world loves soccer' argument. Since when does America take marching orders from the rest of the world?
These are responses to articles like those of Goldberg and Coulter demeaning those who love the game making it seem like we are a distinct minority that can hardly be tolerated. The fact is that we are in the majority globally and this drives some mad.
In most cases, a fan of any sport may get "indignant" when someone who is not a fan tells them why they should not be a fan in the first place. The someone in this case is the author.