A lot of stuff that people say online isn’t necessarily true or untrue. We want room for the messy middle. The concern is when information is outright false, and we know that some of the same people are responsible for amplifying that misinformation again and again. Last fall, a coalition of misinformation researchers found that about half of all retweets related to multiple and widely spread false claims of election interference could be traced back to just 35 Twitter accounts, including those of Mr. Trump and the conservative activist Charlie Kirk. A research group recently identified the accounts of about a dozen people, including Robert F. Kennedy Jr., who repeatedly — sometimes for years — pushed discredited information about vaccines or, more recently, false “cures” for Covid-19.