Which, tbf, the US and UK already have to some degree.
But there is a big difference between the U.K. and America here; in the U.K. if you lose a litigation, you have to pay your opponents legal bills. In America the cases where the loser must pay are very limited with high bars to clear. This means that it’s absolutely possible to bankrupt someone in America with frivolous lawsuits, so long as those lawsuits aren’t bad enough to trigger the limited exceptions.
If a lawyer, doctor, accountant, engineer, or any professional gives you bad or malicious advice, they expose themselves to liability for the results of it. If you want to present yourself as an expert on some topic and expect people to listen to you, put some skin in the game and stand behind what you say. If you can't do that, you shouldn't be advising people on anything.
You might also want to remember that one of the first things Hitler did after getting power was to outlaw any opposition parties and violently break up meetings of any dissenters, then arrest and torture anyone who was promoting anything other than the Nazi party line. Hmm, sound familiar?
Contrary to what is expressed above, Hitler did much more than give speeches. He also gave orders which is a different thing entirely.
Saying "Gee I wish so-and-so were dead" is not a crime in any reasonable democracy. Telling your subordinate "I order you to go and kill so-and-so" is. Do you see the difference? The person following and the person giving the order are both responsible.
Are you arguing that the people who physically pulled the triggers or shoved prisoners into gas chamber do not bear any responsibility? At any point, all that was necessary to stop Hitler was for people to not listen to him. What would help that is providing an environment of healthy dissent, not stifling it.
I also mentioned above specifically that we should hold people accountable for the actual consequences of their speech. How you get from that to "Hitler did nothing wrong" is completely beyond me. Actual consequences mean real things that occur in reality. Not "I think something might possibly happen because of this" or "You dared to contradict an authority so you must be silenced".
The question is where the responsibility lies. Hitler did not elect himself. The responsibility for electing Hitler lies with...the people who voted for Hitler. Where else would you put it?
As to whether someone who "tries to stop him" is a bad person, that depends on what you mean by tries to stop him. One of the benefits of not censoring dissent is that we can hear many different points of view, and hopefully choose better ones. So, of course there is no problem with trying to stop anyone by making a better argument and doing a better job of rallying people to your cause.
If you mean, "Do I think it's OK to murder political candidates as long as I'm sufficiently convinced they'll be evil", no I don't. Keep in mind that there are people who feel about Obama or FDR the way you feel about Hitler and reconsider whether you want to condone murdering anyone you disagree with.
David Icke might not be so cavalier about telling people to burn down cell towers if he could be sued and/or jailed after people took him up on it.
As a general principle, I think we should focus on actual consequences, not imagined, potential consequences.
This has the effect of also encouraging useful dissent. If you disagree with WHO and you turn out to be right, you can be properly credited with it. You are not automatically punished for the crime of daring to disagree with the WHO, and we all benefit from having more accurate, useful information.