For example, it's one thing to express a controversial or unpopular opinion, but it's quite another to engage in hate speech, incite violence, post SPAM, excessive use of straw-man arguments, countering scientific consensus with harmful conspiracy theories, et al. In these cases, allowing such speech to go unchecked can have harmful consequences, and it's important for society to have mechanisms in place to address these issues.
Free speech is important to balance a strong democracy but its not an absolute right. Moderation in free speech is necessary in order to balance the rights of individuals to express themselves with the need to protect the rights and safety of others. Without moderation, the right to free speech can become a license to cause harm and to silence the voices of others.