Of course it was absolutely considered moral and ethical.
There are tons of old articles, books, and treteases on the matter, describing it as perfectly moral and ethical, and how its beneficial to the slaves, who lack agency, are animal like, and are offered "useful work" from their masters who know better, how they are beastly and need the whip to get sense into them, and so on.
That's of course, on top of the fact that slave owners were among the most respected good-standing members of society, and only controversial figures considered them imoral and unethical for owning slave. In fact abolitionists were considered bad people, not unlike today's terrorists and activists.
Theses idea of the morality of being a slave owner, and the superiority and natural right of the owners vs the slaves, is universal in societies that held slaves (as was in societies were royals and lords were above folks reduced to peasants).
Regarding the South, for example:
"What were Southern pastors, preachers, and religious leaders telling their flock? Southern clergy defended the morality of slavery through an elaborate scriptural defense built on the infallibility of the Bible, which they held up as the universal and objective standard for moral issues.
(...)
Reverend Furman of South Carolina insisted that the right to hold slaves was clearly sanctioned by the Holy Scriptures. A fellow reverend from Virginia agreed that on no other subject “are [the Bible’s] instructions more explicit, or their salutary tendency and influence more thoroughly tested and corroborated by experience than on the subject of slavery.” The Methodist Episcopal Church, South, asserted that slavery “has received the sanction of Jehova.” As a South Carolina Presbyterian concluded: “If the scriptures do not justify slavery, I know not what they do justify.”
As Pastor Dunwody of South Carolina summed up the case: “Thus, God, as he is infinitely wise, just and holy, never could authorize the practice of a moral evil. But god has authorized the practice of slavery, not only by the bare permission of his Providence, but the express provision of his word. Therefore, slavery is not a moral evil.” Since the Bible was the source for moral authority, the case was closed. “Man may err,” said the southern theologian James Thornwell, “but God can never lie.”
The Southern Presbyterian of S.C observed that there was a “religious character to the present struggle. Anti-slavery is essentially infidel. It wars upon the Bible, on the Church of Christ, on the truth of God, on the souls of men.”
During the 1850’s, pro-slavery arguments from the pulpit became especially strident. A preacher in Richmond exalted slavery as “the most blessed and beautiful form of social government known; the only one that solves the problem, how rich and poor may dwell together; a beneficent patriarchate.” The Central Presbyterian affirmed that slavery was “a relation essential to the existence of civilized society.” By 1860, Southern preachers felt comfortable advising their parishioners that “both Christianity and Slavery are from heaven; both are blessings to humanity; both are to be perpetuated to the end of time.”
Same for politicians:
William Harris, Mississippi’s commissioner to Georgia, explained that Lincoln’s election had made the North more defiant than ever. As Harris saw things, “Our fathers made this a government for the white man, rejecting the negro as an ignorant, inferior, barbarian race, incapable of self-government, and not, therefore, entitled to be associated with the white man upon terms of civil, political, or social equality.” Lincoln and his followers, he stated, aimed to “overturn and strike down this great feature of our union and to substitute in its stead their new theory of the universal equality of the black and white races.” For Harris, the choice was clear. Mississippi would “rather see the last of her race, men, women, and children, immolated in one common funeral pyre than see them subjugated to the degradation of civil, political and social equality with the negro race.”
More to the point, he noted, abolition meant “the turning loose upon society, without the salutary restraints to which they are now accustomed, more than four millions of a very poor and ignorant population, to ramble in idleness over the country until their wants should drive most of them, first to petty thefts, and afterwards to the bolder crimes of robbery and murder.”
https://www.battlefields.org/learn/articles/why-non-slavehol....