There is a long-running lie that the Irish were slaves and got over it, so African Americans should do too. The lie and its spread have been most thoroughly dissected by the historian Liam Hogan, but this is Frederick Douglass on the subject in the 1840s, via the Project Gutenberg edition of My Bondage and My Freedom. He does not refer to exactly the same lie, that of Irish slaves in the Americas, but clearly there was a similar lie flying around in the 1840s, and he had an answer to it.
It is often said, by the opponents of the anti-slavery cause, that the condition of the people of Ireland is more deplorable than that of the American slaves. Far be it from me to underrate the sufferings of the Irish people. They have been long oppressed; and the same heart that prompts me to plead the cause of the American bondman, makes it impossible for me not to sympathize with the oppressed of all lands. Yet I must say that there is no analogy between the two cases. The Irishman is poor, but he is not a slave. He may be in rags, but he is not a slave. He is still the master of his own body, and can say with the poet, “The hand of Douglass is his own.” “The world is all before him, where to choose;” and poor as may be my opinion of the British parliament, I cannot believe that it will ever sink to such a depth of infamy as to pass a law for the recapture of fugitive Irishmen! The shame and scandal of kidnapping will long remain wholly monopolized by the American congress. The Irishman has not only the liberty to emigrate from his country, but he has liberty at home. He can write, and speak, and cooperate for the attainment of his rights and the redress of his wrongs.
The multitude can assemble upon all the green hills and fertile plains of the Emerald Isle; they can pour out their grievances, and proclaim their wants without molestation; and the press, that “swift-winged messenger,” can bear the tidings of their doings to the extreme bounds of the civilized world. They have their “Conciliation Hall,” on the banks of the Liffey, their reform clubs, and their newspapers; they pass resolutions, send forth addresses, and enjoy the right of petition. But how is it with the American slave? Where may he assemble? Where is his Conciliation Hall? Where are his newspapers? Where is his right of petition? Where is his freedom of speech? his liberty of the press? and his right of locomotion? He is said to be happy; happy men can speak. But ask the slave what is his condition—what his state of mind—what he thinks of enslavement? and you had as well address your inquiries to the silent dead. There comes no voice from the enslaved. We are left to gather his feelings by imagining what ours would be, were our souls in his soul’s stead.
Incidentally, he also compares the singing of slaves in the United States to what he heard in Ireland during the Famine:
In the most boisterous outbursts of rapturous sentiment, there was ever a tinge of deep melancholy. I have never heard any songs like those anywhere since I left slavery, except when in Ireland. There I heard the same wailing notes, and was much affected by them. It was during the famine of 1845-6.