It makes sense because one of our values is freedom of thought. What you believe doesn’t strip you of your citizenship. You can be punished for actions against the county, but you are still an American. For example, Rev. Wright is clearly anti-American. He is still however an American.
I see your point in a legal sense but in my view he is Ameirican in name only.
I believe what makes America is the notion that there is a Creator, that our rights come from him, that the Constitution is the guarantor of those rights and it is the love of and abiding by that notion that makes one an American.
So if a person does not agree with and defend those values, how can he be an American?
JMHO