Don't want to drag this out any further than is strictly necessary, but I don't think you can honestly say that Colston was a bad person in the context of the point in time that he lived.
He did a lot of good for the city of Bristol which is still seen today in terms of the schools and infrastructure that his money helped fund. He didn't need to bequeath money to Bristol, but he did. As a person of power and influence at that time in history, he was probably no worse than any of his contemporaries.
In an 'enlightened' modern world however, people that still think that slavery and people trafficking is acceptable and practice the despicable trade for their own profit and ends should be jailed for life without parole.
Just sayin