Mass murder isn't free speech, because it directly infringes on the rights of other people. To wit, your freedom to swing your fists around in the air ends at my face. Expressions that do not cause direct harm, by their nature, are generally covered under 1A. Calls to commit genocide that don't rise to the level of incitement, for instance, are covered by free speech protections (e.g., nazis marching in the heavily Jewish city of Skokie, IL). Outright lies and yes, defamatory comments, are covered by 1A protections. (In the case of defamatory speech, the government has no course of action; Trump lost a suit brought by E. Gene Carrol for defamation, not a criminal prosecution by the gov't.) Child pornography is not covered by 1A protections, because child pornography can't be created without committing acts that are otherwise illegal. Generally speaking, when the gov't has a legitimate interest in controlling certain forms of speech that are likely to cause harm--such as incitement--principles of strict scrutiny apply; the laws restricting 1A rights are supposed to be as narrow as possible to achieve the stated goals. Prior restraint is also usually not a thing without being very, very narrowly crafted.

Generally, it's authoritarians and reactionaries that want to intentionally blur the lines between speech and actions.