Many people from different political backgrounds will have been surprised to learn that the ardent 19th-century Irish nationalist John Mitchel, formerly of Newry, was a strong supporter of slavery and that he backed the Confederate States in the American Civil War, during which his two sons died fighting for the pro-slavery cause.
As a pupil of Newry Grammar School in the mid-1950s, I was aware that John Mitchel was buried in a Presbyterian church cemetery in the town. In my early teens, I watched each autumn as a massive Apprentice Boys' parade in Newry made its way to a Protestant church in a nationalist area, partly because I loved to follow one or other of the excellent brass bands on the march.
It was only years later that I realised this parade was apparently a quid pro quo for an annual republican visit to the grave of Mitchel, the son of a Presbyterian minister, in a Protestant graveyard in the unionist part of the town.
Mitchel made the news recently when there were calls for Newry, Mourne and Down District Council to rename a street in Newry called John Mitchel Place. Currently, there is an online petition asking the council to remove Mitchel's statue to a place where his "history and context can be more carefully assessed" and to rename John Mitchel Place Black Lives Matter Plaza.
The statues and memorials of other well-known historic Ulstermen are also under threat. Amnesty International wants a name-change for Larne's McGarel Town Hall, which was funded by Charles McGarel (1788-1876), a slave-dealer and sugar plantation owner.
There are also calls to remove the statue of the Co Down polymath Sir Hans Sloane, a co-founder of the British Museum, because he married into a family which owned slaves.
Even King William of Orange has been dragged into the controversy, because he had shares in a company owned by the Bristol slaver Edward Colston, whose statue was dumped in the city's harbour by protesters recently. It was later retrieved from its watery grave and removed to a local museum.
However, Mitchel (1815-1875) was one of the most outspoken supporters of slavery. A member of the Young Ireland group and the Irish Confederation, he was convicted of treason in 1848 and sentenced to 14 years' penal servitude in Van Diemen's land (now Tasmania), from where he escaped to America in 1853.
Mitchel was, in his own right, a remarkable operator. In Ireland, he had already made his name as an activist, author and political journalist, so few people were surprised that, when he reached New York, he established a radical Irish nationalist newspaper, The Citizen, and became a leading apologist for slavery.
He wrote: "We deny that it is a crime, or a wrong, or even a peccadillo, to hold slaves, to buy slaves, or to keep slaves to their work by flogging, or other needful correction."
He also claimed that slavery was inherently moral and "good in itself". He further claimed that slaves in the southern states were better looked after than Irish cottiers and industrial workers in England.
In a blatantly racist remark, he claimed that slaves were "an innately inferior people" and that he promoted slavery "for its own sake".
His views were very unpopular among his colleagues in the Young Ireland movement back home and also among abolitionists everywhere, including those in burgeoning America.
Mitchel was born near Dungiven in 1815 and, when only 19, was awarded a degree from Trinity College Dublin.
He was obviously a bright man and he must have been aware that only a couple of decades before he was born, there had been a concerted and successful campaign to prevent slave ships docking in Belfast, which perhaps makes Mitchel's chilling views on slavery all the more extraordinary.
That Belfast anti-slavery campaign was led by Thomas McCabe, who helped to prevent the formation of a slave ship company proposed in 1786 by prosperous local merchants, including Waddell Cunningham and his business partner, Thomas Gregg.
Their plan was to ship goods to the Gold Coast in Africa and fill their vessels with captured slaves, who would then be transported to the West Indies and offloaded. The vessels would then be filled with sugar and brandy destined for Belfast.
Slaving was a murky business at that time for other ports, such as Bristol. However, Waddell Cunningham, a leading citizen of Belfast and a former chairman of the Chamber of Commerce, and his backers had no scruples. Cunningham owned sugar estates in the West Indies and, in 1775, he established, along with Gregg, the largest shipping company in New York.
Back in Belfast, Waddell Cunningham was a formidable opponent of those who campaigned for the abolition of slavery. He was a successful entrepreneur and a merchant and banker.
He was also a member of the Ballast Board from its inception in 1785 until his death in 1797. The Ballast Board was the precursor of the Belfast Harbour Board, which continues to develop the port to the present day.
Cunningham was a leading member of the Volunteer movement and opposed the Society of United Irishmen.
After his death, he was buried in Newtownbreda with full military honours, supplied by the Belfast and Castlereagh Yeoman Cavalry and Infantry.
A local newspaper obituarist described him as having "a life of ardent and active exertions" and a man who used his fortune "in the most useful manner and to the most generous purposes". Obituaries in those days often omitted their subjects' failings.
In his prime, Cunningham had enormous influence in Belfast and the symmetry of his plan to form a shipping company to transport slaves was inescapable. But he had reckoned without the conscientious objections of other leading Belfast citizens who were vehemently opposed to slavery.
They included Thomas McCabe, whose home, The Vicinage, was then on the site where St Malachy's College now stands.
McCabe hosted meetings of the Belfast Charitable Society and the Society of United Irishmen there, as a member of both organisations.
McCabe was a goldsmith and watchmaker with a business in North Street. He was also a radical member of First Presbyterian Church in Rosemary Street at a time when the Presbyterian Church was in the vanguard of liberalism.
When Waddell Cunningham held a meeting in the Exchange and Assembly Rooms in Waring Street in 1786 to establish a Belfast slave ship company, Thomas McCabe walked the short distance from his shop in North Street to join the meeting.
He made an impassioned speech against the plan and uttered a warning which still echoes down Irish history today: "May God wither the hand and consign the name to eternal infamy of the man who will sign that document."
His speech caused a great stir and, in the prevailing climate of Protestant liberalism, it helped to carry the day and prevented the formation of a slave-trading company in Belfast. Later, McCabe wrote to Dr William Drennan, another prominent Belfast citizen, to tell him how that plan to establish a Belfast slave-ship company had been aborted.
Drennan was also a man of great ability who had many interests. One of his claims to fame was a masterly outline on how to deal with a pandemic - an achievement which has a remarkable resonance for our world today.
Some of the United Irishmen were so opposed to slavery that they refused to eat sugar or drink rum from the West Indies because of the association with the slave trade.
To underline the prevailing opposition to slavery in Belfast, in 1791, the famous freed slave Olaudah Equiano, who wrote a bestselling book about his experiences, was invited to Belfast by the United Irishmen and given a warm reception. He reputedly sold nearly 2,000 copies of his book The Interesting Narrative of the Life of Olaudah Equiano, or Gustavas Vassa, the African, during his stay, when he lodged with the draper, United Irishman and radical newspaper editor Samuel Neilson.
When Equiano left Belfast, Neilson's Northern Star newspaper (founded in 1792) continued to give wide coverage to anti-slavery propaganda.
Despite the best efforts of people like Thomas McCabe, Mary Ann McCracken (sister of the United Irishman Henry Joy McCracken) and many others, a large number of Belfast cobblers continued a brisk trade making broader-fitting shoes for slaves. Other traders supplied commodities for slave owners in the West Indies and elsewhere.
In 1807, the anti-slave campaigner William Wilberforce was successful in getting legislation passed in the House of Commons to abolish slavery.
In 2007, the great-great-great-great grandson of William Wilberforce, also called William, visited First Presbyterian Church on the 200th anniversary of the abolition of slavery.
He brought with him an iron casket presented to Wilberforce by former slaves in recognition of his dedication to the abolitionist cause. It was forged from the shackles that the slaves had worn on sugar plantations.
In the current debate about race and the Black Lives Matter movement, it is worth noting that because the efforts of Thomas McCabe and many other anti-slavery campaigners in the latter decades of the 18th century, Belfast retains the noble record of being one of the few major ports in the British Isles to have turned its face against the slave trade.
The story of Thomas McCabe, the radical Presbyterian from Belfast, and the challenges which he and his colleagues in the United Irishmen overcame to keep slave ships out of Belfast, shows how complex that struggle was.
Modern attitudes to difficult historical subjects need to take account of what actually took place during those days if people are to make informed judgments about the best way to handle the dark residue of the past.
Alf McCreary is the author of Titanic Port: An Illustrated History of Belfast Harbour