It is their fortune to fall into the hands of rational and benevolent owners

[Their removal was] a species of dispensation of Providence in their favour, to bring them to a better state of civilization than they could attain to in their domestic residence; and such it must undoubtedly prove in a very high degree, when it is their fortune to fall into the hands of rational and benevolent owners.
~ Henry E. Holder (1788)

A FURTHER scriptural evidence

A FURTHER scriptural evidence, that the conduct of Joseph in purchasing so many millions of his fellow-creatures, and reducing them to the conditions of Slaves, met the entire approbation of God, and was therefore perfectly consonant to the sacred laws of Nature, is that remarkable declaration of the Word of God, registered in the First Book of CHRONICLES.
~ Raymund Harris (1788)

Rescuing many millions of Africans

[The Slave Trade is a] generous disinterested exertion of benevolence and philanthropy, which has been the principal means of heaping wealth and honours on the Europeans and Americans, and rescuing many millions of Africans, as brands from the fire, and even compelling them to the enjoyment of a more refined state of happiness, than the partiality of fate has assigned them in their native state.
~ Anonymous (1773)

Some gentlemen may … object to the slave trade as inhuman and impious

Some gentlemen may … object to the slave trade as inhuman and impious; let us consider that, if our colonies are to be maintained and cultivated, which can only be done by African negroes, it is surely better to supply ourselves … in British bottoms.
~ Temple Luttrell (1777)

If few die … the voyage is lucrative

The investment risked in entering this business is small … . A cargo may consist of sixty slaves … . If few die … the voyage is lucrative … . More than 25,000 slaves have arrived for use in agriculture this year, 15,000 entering Bahia alone and 10,000 at Rio.
~ José da Silva (1781)

There are many more positive conditions of slavery

There are many more positive conditions of slavery than that of one man being the property of another, and being subject to his will and dominion: and if such positive conditions be necessary in every association of men, both under a civilized government as states but little removed from that of nature—if various ranks and orders of men be necessary, that the political wheel may go round, that the purposes of social life be more completely fulfilled, … [let it be admitted.]
~ Jesse Foot (1792)

AS COMFORTABLE A STATE, AS THE LOWER ORDERS OF MANKIND

I consider the Negroes in the British West India Islands to be in as COMFORTABLE A STATE, AS THE LOWER ORDERS OF MANKIND IN ANY COUNTRY IN EUROPE.
~ Captain McCarty (1792)