From Katebrygge to Feline Court in barely half a millennium.
There was once a school teacher who, when asked by a pupil “Why is that flower called a daffodil?” always replied “Well, it had to be called something, and hippopotamus had already been used.”
Or you could say that by slave trader you mean someone who has personally put a manacle on a slave's wrist or personally wielded a whip — which Edward Colston certainly did not. Conceivably, he didn’t even quite understand the awful reality that lay behind the pounds, shillings and pence on his ledger sheets.
The most frequently made argument is that the evil men do lives after them while the good is oft interred with their bones and it should be possible to memorialize Colston as a philanthropist while deploring him as a slaver. The crime of kidnapping black people and taking them to places where they will be literally used like cattle is mitigated if you use some of your profits to set up schools and buy cottages for white people. This reminds one of the story of the man who murdered his mother and father and asked for mercy on the grounds that he was an orphan.