It does make a lot of difference if Americans are in America, or if they are in foreign countries.
In the latter, unless they can be extradited, kidnapped by US Marshals, which they are now authorized to do, or taken as prisoners by the US military; *and* they are engaged in providing support to an enemy of the United States; there is little else the government can do but to kill them as if they were enemy combatants.
Holder actually advanced a reasonable inclusion to the presidential ability to order the killing of an American overseas, that they must be an “essential part of an imminent attack against US forces or America itself.”
That is, if they are an American journalist who happens to be blown up while attending a conference of top al-Qaeda leaders, they are not particularly targeted, they are collateral damage.
However, if the purpose of the bomb is to take them in particular out, they must be actively engaged in treason, and a principal to at least the possibility that an attack is about to be carried out.
If they were killed by US soldiers firing guns it would not be considered murder, even if the enemy was known to be an American. The only difference is that a drone is a risk-less, and totally voluntary attack. That is not a big enough difference to matter.
Arguments have been made for years that bomber aircraft crews are committing war crimes by bombing, in that if their side has air superiority, the risk to them is minimal, and they cannot see those they kill. So they are also acting in an entirely voluntary manner.
If someone is an enemy combatant they have to be in combat or have been in combat against US Forces. The people that our government has killed with drone strikes have not been. Our government has murdered US Citizens.
As long as we allow the government to define the actions that they can do we are all eventually going to become a target.