Since the OP was asking about laws in General Questions, the basic assumption would be that he was asking a legal question rather than soliciting personal opinions about what would have happened. The question you posit would have been non-factual, and in any case your response at best was a personal opinion rather than a factual response.
I note that some German agents actually planning sabotage in the US were tried and executed, while others were simply imprisoned. They weren’t lynched, as you imply Tokyo Rose would have been.
There was no sedition laws operating during WWII. The Sedition Act of 1918 was repealed in 1920. The closest was “The Alien Registration Act, popularly known as the Smith Act, … enacted on June 29, 1940. It set criminal penalties for advocating the overthrow of the U.S. government by force or violence and required all non-citizen adult residents to register with the federal government.”
This is a much narrower prohibition than sedition, and much more focused than the 1918 act. There had been a backlash after the abuses under that act. And the isolationist movement still had huge numbers of supporters in 1940, so merely talking against the war wasn’t going to fly. Speech in America during WWII was far more open than in any other belligerent.
I’m old enough to have known men who served in WWII. Generally speaking, they regarded military organization as such a gigantic clusterfuck that nothing surprised or even interested them.
On a related note, the Australians who served in the Japanese information service did make creditable claims that they saw part of their role as passing on to Aus Intelligence anything the learned that was important or valuable. Naturally (see paragraph above), Aus intelligence weren’t listening at all. Post war, the Australians were treated rather worse than the Americans.
Prosecuting people for revealing, or suggesting at least, secrets in ways and venues the enemy might not pick up on is just calling more attention to it. If you can be reasonably sure it was done out of stupidity or over eagerness it might be better to warn them to shut up.
Maybe this is affected by an implicit assumption it’s like now and anything juicy like that which appears in media is going to be picked by other media, be all over the internet and no way the enemy would miss it. But by all evidence Japanese intelligence never picked on the the Johnston story or drew any conclusion about the security of their codes if they did.
Another such case was the public statement by Congressman Andrew May in 1943 after a tour to the war zone saying the Japanese were setting their depth charges too shallow in attacks on US subs. Some news outlets thoughtlessly reported that also. The commander of US subs in the Pacific later estimated that revelation cost 10 submarines, but again there’s no actual evidence the Japanese picked up on it, but prosecuting May or the papers would probably have increased the chance of it coming to their attention.
OTOH Americans allegedly participating in propaganda efforts from Japan didn’t risk any US secrets the Japanese didn’t already have. And it wasn’t possible to even consider prosecuting till the war was over. And it was assumed to be fully intentional attempt to harm the US unlike the other cases. Still a judgement call though whether there should have been an attempt to find and prosecute a real ‘Tokyo Rose’ after the war but not do anything to May, particularly.
But since it was efforts from Japan seems no doubt that was treason if you had the right person and could prove it wasn’t coerced. ‘Public information’ is secondary, and anyway as was mentioned some TR broadcasts apparently benefited from information the Japanese obtained through espionage (I don’t know if the details are known though how they got that info).
The cases were different. Haw-Haw was consciously and deliberately aiming to undermine morale and promote the enemy’s cause, having acquired a new British passport to enable him to get to Germany to do so.
Wodehouse was naive and self-centred enough not to see how otherwise innocuous comments on his internment might be misused and would be received by his compatriots in the middle of the Blitz. Dishonourable but hardly criminal.
If anyone had tried making pro-enemy broadcasts from within Britain, by some pirate station, they would probably have been dealt with as “giving aid and comfort”, but no doubt it would have depended on exactly what they said. “Soft” propaganda aimed at civilians would be rather different from, say, inciting munitions workers to sabotage their factories or encouraging troops to desert. Treason prosecutions were very rare, when lesser offences were more easily prosecuted (and attracted less news coverage while newsprint was so heavily rationed).
The Espionage Act of 1917 was still in force according to the linked paper, and was used to successfully prosecute and imprison William Dudley Pelley, a leading American Fascist and organizer of the “Silver Shirts”.
"After the United States entered World War II, Pelley charged that Roosevelt had imposed an oil embargo on Japan in order to force it into war, maintained that Roosevelt’s policies had led the nation to the “verge of bankruptcy,” accused Roosevelt of instigating the war in order to save his faltering New Deal economy, and predicted a swift and glorious victory by the Axis. At Roosevelt’s insistence, Pelly was charged under the Espionage Act of 1917 with making "false statements with intent to interfere with the operation or success of the military or naval forces of the United States or to promote the success of its enemies.’’
As I said above, if the government wants a show trial to convict you it will figure out a way and in the right environment the courts will back it up. (also see Korematsu v. United States.)
Though Roosevelt’s desire to get rid of Pelley and the Fascists was understandable, he had also lived through the years since WWI. He’d seen Palmer’s Red Scare, the persecution of socialists, the rise of cults around Huey Long and Father Coughlin, and the near-collapse of democracy during the Depression. He knew he needed to look different from those anti-American actors, to bolster the ideals of American democracy and free speech. The entire war was pitched as the opposite of fascism, an exercise in proving that democrat ideals were the superior ideology. He recognized that allowing speech at its most open without overt government crackdown was crucial, even if it pinched him at times. And despite this one very early example he adhered to it throughout the war.
I don’t disagree with this, and previously emphasized limitations on prosecution.
Still, the examples provided show that American fascists (the more influential ones, anyway) didn’t have a free ride when it came to undermining the war effort and giving comfort to our enemies.
At least for the first few months after Pearl Harbor, when public reaction was highest.
After that government action took place mostly behind the scenes. They threatened and blustered a lot but did very little because they didn’t want anything to become public. After the war none of it mattered, so they didn’t pursue any prosecutions.
They kind of were, actually. They were hustled into a secret military tribunal partly to protect the FBI from embarrassment (Hoover had gone to great lengths to portray the FBI’s arrest of these agents as intrepid detective work, when in fact one of them just turned himself in and led them to the others) and partly because FDR wanted the death penalty, which almost certainly would not have been available under any existing US legal system for the little that these agents had been able to accomplish. To the government’s credit, they did allow a habeas corpus petition to the Supreme Court, but the Court basically spent a day or two figuring out the least damaging way to capitulate. FDR told his AG (potentially with the expectation that the Court would hear about it) that the administration was not going to turn over these agents to the Court’s US Marshals, regardless of any writ.
A less charitable way of describing events is that after indicting, intimidating, or otherwise silencing his loudest critics, there was less need for further action. The defendants at the mass Smith Act trial were a bunch of cranks, but the group happened to include a lot of Roosevelt’s longtime opponents; putting thirty of them on trial for sedition* goes a long way to send a message. The administration also revoked Father Coughlin’s postal privileges and convened a grand jury against him around this time. And before Pearl Harbor, the feds had used the Smith Act to break a labor union at a defense contractor. They don’t necessarily have to keep prosecuting others once it’s clear that you shouldn’t put your free speech rights to too much of a test.
Plus there was the suppression of dissent accomplished by the quiet mass intimidation campaign against Italian immigrants and the highly public internment of Japanese-Americans (imprisonment of a racial group kind of hollows out the anti-fascist message they may have wanted to send to the rest of the world, too).
*The Smith Act may have been narrower than traditional sedition on its face, but there was little evidence that these defendants were actually advocating the destruction or overthrow of the government.