Typical BS spin... you are also factually incorrect.
The FBI/CIA did not have 'secret codes' that were later declassified - you are referring to sources such as the Mitrokhin archive and various other KGB files that have been recieved long after their execution. This information confirmed that Julius Rosenburg was involved in some low level spying, and failed to mention Ethel Rosenburg at all - so it is more than likely that she had only a passive role. What we do now know is that the information Julius Rosenburg passed was insignificant compared to the real meat and bones intelligence the KGB got on the atom bomb from their british sources.
The reality is that the trial of the Rosenburgs was a politically motivated show trial, he was an ideolgically motivated jewish communist - insignificant in terms of intelligence passed - but symbolic for the anti-red paranoia of the time.
The FBI knew they had little case against Ethel Rosenburg but were determined to prosecute and get the death penalty for her in order to get leverage on Julius to co-operate. They were convinced they could 'break' the couple and get useful information from them.
The main witness against them had a personal grudge and was part of the spy-ring, the FBI coached every witness to perfection.
They were both offered clemency, if they would confess all and implicate others. They didnt, so were executed. The public were shocked by the severity of the sentances, its extremely unusual for espionage cases to result in a death sentance. The FBI were shocked that they never broke them.
Of course, don't let any of the grey blurriness of real life interfere with your revisionist black and white view of history. I mean, that might mean that the real present world isn't black and white either !