Actually, when the Rosenberg case was going on, liberals marched in demonstrations to support them.
Iva Toguri (Tokyo Rose) eventually served 6 years in prison for treason, but was later pardoned by President Ford.
As to Robert E. Lee: He lived at a time when Americans considered the US to be a union of sovereign states and it was widely believed that states had the right of secession. Lee believed that his country was Virginia.
When the Civil War was still in its early stages, Lee was offered the command of the Union Army, but felt that his higher duty was to his “country,” Virginia. He resigned his US commission and became an advisor to Confederate President Jefferson Davis.
Lee served in that capacity for about a year before being induced to take command of the Army of Northern Virginia.
To call Lee a traitor, or to accuse Confederate figures of treason is a vast oversimplification. It is now popular among ignorant leftists, but not supportable by the nuances of the Civil War.