Can freedom of speech be denied/restricted? when? why is the freedom of speech necessary in a democratic society? i have an idea of what i want to say but i just want a second opinion.

Freedom of speech is regularly denied and restricted in both democracies and undemocratic states across the country. Even in countries like the United States there have been attempts throughout history to restrict free expression due to particular reasons usually related to national security such as during the red scares in the first half of the 20th century. Freedom of speech is believed to be necessary in a democracy to push new ideas and prevent any voice from being silenced by political powers.