Final answer:
John Stuart Mill saw the limitation of freedom of thought and expression as dangerous because it stifles the exchange of ideas, hindering individual and societal development. The Supreme Court has placed limits on free speech in extraordinary circumstances, but there is a continuous debate on how to balance security needs with preserving freedom of expression.
Step-by-step explanation:
The danger John Stuart Mill sees in limiting and trying to limit freedom of thought and expression is that it can suppress the exchange of ideas, which is crucial for personal and societal progress. Mill believed that individuals should have the right to explore their own idea of "the good" and that society benefits from a diverse range of opinions and discussions, even if some are unpopular or go against the consensus. Liberty in his view was paramount, and only direct harm to others could justify restrictions on personal freedom. Therefore, legal measures and cultural norms must protect this personal liberty robustly.
The U.S. Supreme Court has at times limited the First Amendment right to free speech, as in instances where speech presents a "clear and present danger" to national security. However, current standards indicate that the Court is careful to distinguish between abstract criticisms of the government and explicit incitements to violence. The ongoing debate revolves around how to balance the need for security and the value of free speech, especially during times of conflict or concerning governmental whistle-blowing and journalism.
Mill's advocacy for broad freedom of expression warns against the risk of silencing dissenting viewpoints, which are necessary for a functioning democracy and for the intellectual growth of individuals. Limitations on speech can also lead to the prohibition of certain ideologies, which goes against the foundational liberal values that deem personal liberties—including the liberty of expression—highly important.