Before I start (Source: wikipedia):
The Purple Heart is a United States military decoration awarded in the name of the President to those wounded or killed, while serving, on or after April 5, 1917, with the U.S. military.
There are other awards for the “mass slaughter” Plath mentions; the Purple Heart ain’t it.
Now to answer the question: both the slaughtered combatant and executed criminal are enemies of the State. Death is the final argument, ultima ratio for or against anything meaningful in this world* . Like it or not, the State happens to be a thing with meaning.
Both combatant and criminal are willing or have already used violence against the State and the people within it’s borders. The State represents not only present security, but the history and future of you and your people.
Yesyes, the modern system does not seem to care much about our history and future. We are not kneejerk anarchists here: there exists worse things than even a democrat. Does a Muslim jihadist care more about your society than the Machiavellians in Congress? Does the serial rapist/murderer care about your personal rights more than the mean ole’ cop?
With combatant and criminal the choice comes down to us and them; if your mind isn’t completely unhinged the choice is a simple one.
Perhaps there is a case for the legal system and global geopolitical structure being “arbitrary” and “personal whim,” but I don’t see it. Rather, I see the condemnation of arbitrariness and capriciousness better applied to a suicidal writer of shitty poetry.