Well, if you travel to a war zone and join the other side, you should be afraid.
Joined what other side? We are not at war with Syria. We do not even belong there. He did not join ISIS or Al Qaeda so he is not a terrorist. He was never designated a terrorist by any EU or US agency. He took an unpopular stance which was opposite of our stated position in Syria. He did that by reporting on the war from the Syrian perspective, but nothing about that was illegal. Why do we have any American service members on the ground in Syria? Lebanon, Syria, Jordan and Iraq are countries established by the French and British to divide up the Middle East colonies. Why do we care if Assad runs Syria? They are no threat to us. Assad is friends with Iran, so we are effect fighting a proxy war against Iran. But, it has been suggested that Assad would agree to evict Iran and not allow Iran to move oil and arms through Syria as terms to end fighting. All sides oppose ISIS. This mess is Obama’s Arab Spring, that’s how long it has gone on.
None of that matters, because the real issue is; did a US three letter agency attempt to kill an American citizen overseas. If the US citizen was placed on a kill list, that is illegal. The rest is just window dressing.