Speaking of the death penalty, were the executions of Julius & Ethel Rosenberg in 1953 "justified," considering that they had never killed anyone?

The Rosenbergs allegedly committed an act of espionage against the USA, and supposedly received a fair trial, were judged guilty and eventually executed for their crime on June 19, 1953, amid much controversy and public protest.

To this day, surviving relatives of theirs continue a fight to clear their names and have them retroactively exonerated.

In the 21st Century, they probably would not be executed for such a crime, as no actual murder was committed by them. So, my question is, considering the time period and the threat to Americans of living with the prospect of a Nuclear War with the USSR constantly hanging over their heads, was their execution a “justifiable act” for that time period, or an act of desperation on the part of the USA, to try to prevent future acts of espionage.

FBI Director John Edgar Hoover termed their act, “The crime of the Century.”