Simple, explicit, appealing and emotional arguments and messages beat out complex, tacit, unattractive, and logical ones.
Messages with massive organisation and resources behind them can dominate disorganised or uncentralised attempts to counter them.
Attempting to reput or fact-check specific claims operates relatively poorly.
The consequence has been that many regimes, and philosophers, including those who generally promote free speech, such as John Stuart Mill himself in "On Liberty", put conditions and limitations on the concept:
It is a piece of idle sentimentality that truth, merely as truth, has any inherent power denied to error, of prevailing against the dungeon and the stake. Men are not more zealous for truth than they often are for error, and a sufficient application of legal or even of social penalties will generally succeed in stopping the propagation of either. The real advantage which truth has, consists in this, that when an opinion is true, it may be extinguished once, twice, or many times, but in the course of ages there will generally be found persons to rediscover it, until some one of its reappearances falls on a time when from favourable circumstances it escapes persecution until it has made such head as to withstand all subsequent attempts to suppress it.