In most (if not all) of the EU, an immigration officer being presented a native passport has exactly two choices: a) let the person in, b) get the police to arrest him on the spot. In both cases the person is under the local jurisdiction.
It seems the United States has a legal gray area around its borders, and a very black area outside of its borders (think Guantanamo). There are reported cases of people being detained or harassed. So being a US citizen doesn't let you travel worry-free either.