The first phase of the British empire was roughly from the time of Queen Elizabeth to the start of the Seven Years War in 1754 (or up to 1688 if you want to use the Glorious Revolution as a division point). This is precisely the period when the British were among the world's most active and enthusiastic slavetraders. The abolition of the slave trade in the British Empire was obviously a bright point in its history, but it's worth pointing out that this happened two hundred years into the British Empire's lifespan, not at the beginning.

The goal of the British Empire, as with every empire, is to exploit the empire to the benefit of the ruling country. Everything else is white washing.