At least in the US, free speech is most free within public forums. But even then we already define some speech that is too dangerous if it's known to lead to poor outcomes. You can't yell fire in a crowded room, not because yelling fire is inherently a crime, but because it's going to incite people to a detrimental ends.
Plus social networks don't have a constitutional obligation to be town squares where free speech can spread unfettered. You have to draw a line somewhere. And as the people who write the algorithms that can amplify or bury content on these networks, I think it _is_ our obligation to at least set parameters on what constitutes good/healthy content interactions on these social platforms and what doesn't. The ML algorithms have to optimize over some loss function.
Additionally, the idea of 'clear and present danger' has been modified within the past 100 years since the said court case. The Supreme court since then has stated: "The government cannot punish inflammatory speech unless that speech is 'directed to inciting or producing imminent lawless action and is likely to incite or produce such action'". Said definition has changed and depends upon situations, where some action is imminent or "at some ambiguous future date".[1]
[0] https://en.wikipedia.org/wiki/Shouting_fire_in_a_crowded_the... [1] https://en.wikipedia.org/wiki/Imminent_lawless_action
This phenomenon is mirrored elsewhere as well where small interventions can lead to big impacts: see suicide rates in Britain after removing carbon monoxide in their house gas. Initial friction (or means reduction in that research) can drive change.