You can be nostalgic for something without wanting it back, like an ex girlfriend you wouldn't look twice at today, but who was the love of your life at the time.
I don't know if you read the whole article, but it referenced Britain's part in the Transatlantic slave trade without bothering to mention that it was Britain that ended it with force, or that slavery is still practiced in many parts of the world today. In fact it's very easy to point to the British Empire as the cause of slavery (it wasn't) while ignoring the part many countries/peoples/tribes in Africa and the Middle East took in starting and facilitating that trade.