Misinformation
The spreading of misinformation on social media has had a corrosive effect on our trust in institutions.
Unless you want to eliminate freedom of speech, there is no way to use the legal system to prevent misinformation spreading. The only way to counter its influence is to make it taboo.
While misinformation is consistently called out by the political opposition, it is often embraced by the side that it favors due to in-group bias. This needs to be taboo in modern culture, so that anyone who uses misinformation, or even suggests its use, becomes persona non grata to their now-former in-group, and cannot immediately find another home and income stream by joining the opposition.
Propaganda often takes the form of misinformation, but it can also contain true information that promotes a specific ideology. It is usually state-sponsored, but billionaire-sponsored capitalist propaganda has been become increasingly prevalent in recent years.
See Misinformation, Propaganda, and Propaganda Techniques on Wikipedia.