“England would sink any slave ship it found on the high seas’
Not the case. A ship of the Royal Navy would capture a slave ship. Put the crew in irons, put a prize crew on board and sail the ship to a port in West Africa to off load the slaves. Then the ship would be sold and the officers and crew on the warship, that captured the slaver, would divide up the sale money.
Sinking a slave ship would mean no extra money in the pockets of the officers and crew of the English ship.
You’re right. Should have said ‘take’ instead ‘sink.
Point is the same in that slavery was already considered in a negative light.