One of the biggest brainwashing techniques used and exposes the true gullibility of people to accepting such nonsense from their government.
Most obvious in the United States of America. See Brainwashed.
People are brought up with the thought the U.S. is clearly better than everyone else in the world and all that crap about how it's the "greatest country in the world" even when the people saying this have never been outside the U.S.
No matter how many bad things our government does, they will defend them because, it's their home country. We saw this when the people didn't think twice about the Patriot Act.
This is why people in America let such war criminals stay in power and don't even bother trying to shake the corruption. Their indoctrination through youth and don't even think about it, they see everything completely one sided. They will always make excuses how this is the land of the "free" and it's not a communist country as if that means the U.S. is completely free of corruption and imperialism.
Governments are not the only example, it happens in religion too. Especially if you are raised in a specific religion and taught the mindset, it is clearly blind patriotism when thinking one sided and not looking at the full table and thinking rationally and having second thoughts.