According to William Wilberforce, what were the evils within/causing the slave trade?
Wilberforce objected to the inhumanity of the slave trade, which he held as incompatible with the Christian values he and his fellow members of the "Clapham sect" were attempting to instill in British society. While he, like most liberals of his time, had a laissez-faire attitude toward business, he was also deeply concerned with the acquisitiveness he saw, and for him, the ultimate manifestation of this was the slave trade, which put profits over humanity.
Aside from the violence and inhumanity, Wilberforce and other like-minded reformers also saw it as a corrupt business that operated under government protection due to the inordinate influence of West Indian planters and Liverpool merchants. As an evangelical, he thought it was a stain on the British nation that could not be tolerated.