Treason is a crime. Crimes are dealt with by arrest, trial, conviction and sentencing.
Responding to purported treason by assassination is a cowardly, banana republic approach.
All those poor Confederate soldiers in Picket's Charge. They should have been arrested, not assassinated by Federal marksmen with unfairly-accurate rifles.
It is a statistical certainty (p 10e-1111111) that anti-Nazi German soldiers and civilians were killed by US forces during WW2.
I don't like the government having too much power, but I'm not sure I understand why the ACLU is getting involved in this if it is not being done domestically against American citizens. What's done in war time on foreign soil against non-American citizens doesn't seem to fall within the domain of the American Civil Liberties Union.
It is easy to understand, once you realize that they are on the other side.
In 1750 Issac Newton became discouraged when he fell up a flight of stairs.