photo: The KKK marches down Pennsylvania Avenue in Washington, D.C. in 1926.
Contributing to criminal chaos of the 1920s was the sudden rise of the Ku Klux Klan, or KKK. In the early 1920s, membership in the KKK quickly escalated to six figures under the leadership of “Colonel” William Simmons and advertising guru Edward Young Clarke. Robed members of the KKK marching down Pennsylvania Avenue in Washington, D.C., with American flags and the U.S. Capitol in the background.
By the middle of the decade, the group boasted several million members. The crimes committed in the name of its bigoted beliefs were despicable—hangings, floggings, mutilations, tarring and featherings, kidnappings, brandings by acid, along with a new intimidation tactic, cross-burnings. The Klan had become a clear threat to public safety and order.
While you have a point about how the the 1st Amendment protects freedom of speech. And there are current day examples of the UK government deciding that people protesting against genocide are actually terrorists because of loose, arbitrary definitions. And further points could be made on how in an ideal world, the government should not be allowed to restrict speech.
There is also another point. This picture shows not simply a demonstration of free speech. It also shows a threat of violence and death at a time when this organization was very much involved in acts of violence and murder. Do we really think that the KKK should have the right to implicitly say that they will murder you? Or to have a show of force for how easy it would be for them to murder you?
Right now in the USA, you do not have the right to burn an Israeli flag. That is not considered free speech, it is considered hate speech. If protestors say genocide is bad, they can be arrested and maybe even charged with hate speech. But if the KKK were to march in DC again, there would be a police escort and reporters talking about the 1st Amendment.
Who watches the watchmen? Who determines which groups are marching for true expression and who are marching as a 'show of force for how easy it would be for them to murder you?' It's too much power to give to any group or body, hence why free speech and freedom of assembly is protected. Is it constantly challenged? Sure, another privelage of being an American. You can lobby congress that this damn rock and roll is corrupting the youth and needs to be censored. It doesn't mean you are right, no matter how 'virtuous' your cause.
"I disapprove of what you say, but I will defend to the death your right to say it" -- Evelyn Beatrice Hall. This is the bedrock of our liberty.
If this is what you belive, then you should really be motivated to action by the fact that we aren't allowed to burn Israeli flags in the USA.
Also, what would constitute hate speech or a threat of violence?