I don’t have time to read the whole speech right now, so forgive me if I have missed something relevant to this comment.
The idea of a Black abolitionist addressing a Fourth of July celebration is slightly comical.
From 1776-1782, the British Army promised emancipation to any American slave who joined the British Army.
The Brits kept their word, even after they lost. They transported all former slaves by ship to British controlled Canada.
Well, there is certainly nothing comical about Douglass' remarks. They are as serious as any words spoken in American history.