I also feel that there is no absolute way to determine what is good speech and what is bad speech, yet I also realize that the distinction exists.
Sometimes, there are clear markers. Supporting or promoting acts of violence is a poor fit for civil societies. The same can be said for other forms of harm. Yet I also view the use of speech to suppress speech as being a danger to civil societies since the intent is to discourage discourse.
Other cases are more ambiguous, mostly because I would like to live in a fairy tale world where facts and reason will win the day. This is land where others can say things that I find reprehensible and vice versa so that we can eventually arrive upon the truth. The freedom of speech is necessary in this case because we all have our preconceived notions, some of which will ultimately prove to be wrong. If the preconceived notions of individuals and societies are not challenged, it will be nearly impossible to arrive upon the truth.
The thing is that we don't live in that fairy tale world. The words of some people have more weight. That may be due to social status, connections, wealth, or other factors. Other people intentionally convey falsehoods in order to manipulate outcomes to reflect their motivations. People are also more likely to be swayed by emotion than reason, or to manipulate emotions to override reason.
Where does that leave us? I really don't know. Perhaps the freedom of speech should be regarded as an aspiration rather than as an absolute.