including the subject of slavery. Such a vindication would need, itself, to be vindicated. It would add insult to injury. Not even an old-fashioned abolition meeting could vindicate that right in Boston just now. There can be no right of speech whereany man, however lifted up, or however humble, however young, or however old, is overawed by force, and compelled to suppress his honest sentiments.
http://mistera.co.nf/files/douglass_plea_for_free_speech.pdf
Read the whole essay. It's very short and very enlightening.
there doesn't seem to be anything here