Just present a single Quran verse or sahih hadith that clearly states that slavery is wrong and should be abolished.
By extension the founders of the US are equally culpable because they owned slaves.
And the Bible? The Bible and slavery - Wikipedia
Matthew 18:21-35: Jesus' Parable of the Unmerciful Servant, wherein Jesus compares the relationship between God and humankind to that of a master and his slaves. Jesus offers the story of a master selling a slave along with his wife and children.
Matthew 20:20-28: A series of remarks wherein Jesus recognizes it is necessary to be a slave to be "first" among the deceased entering heaven.
Matthew 24:36-51: Jesus' Parable of the Faithful Servant, wherein Jesus again compares the relationship between God and humankind to that of a master and his slaves.
The Quran? 2:177
Khalifa
Righteousness is not turning your faces towards the east or the west. Righteous are those who believe in GOD, the Last Day, the angels, the scripture, and the prophets; and they give the money, cheerfully, to the relatives, the orphans, the needy, the traveling alien, the beggars, and to free the slaves; and they observe the Contact Prayers (Salat) and give the obligatory charity (Zakat); and they keep their word whenever they make a promise; and they steadfastly persevere in the face of persecution, hardship, and war. These are the truthful; these are the righteous.
Yusuf Ali
It is not righteousness that ye turn your faces Towards east or West; but it is righteousness- to believe in God and the Last Day, and the Angels, and the Book, and the Messengers; to spend of your substance, out of love for Him, for your kin, for orphans, for the needy, for the wayfarer, for those who ask, and for the ransom of slaves; to be steadfast in prayer, and practice regular charity; to fulfil the contracts which ye have made; and to be firm and patient, in pain (or suffering) and adversity, and throughout all periods of panic. Such are the people of truth, the God-fearing.
Pickthal
It is not righteousness that ye turn your faces to the East and the West; but righteous is he who believeth in Allah and the Last Day and the angels and the Scripture and the prophets; and giveth wealth, for love of Him, to kinsfolk and to orphans and the needy and the wayfarer and to those who ask, and to set slaves free; and observeth proper worship and payeth the poor-due. And those who keep their treaty when they make one, and the patient in tribulation and adversity and time of stress. Such are they who are sincere. Such are the God-fearing.
"Progressive Muslims"
Piety is not to turn your faces towards the east and the west, but piety is one who believes in God and the last day, and the Angels, and the scripture, and the prophets, and he gives money out of love to the near relatives, and the orphans, and the needy and the wayfarer, and those who ask, and to free the slaves, and he holds the assembly, and he contributes towards betterment; and those who keep their pledges when they make a pledge, and those who are patient in the face of good and bad and when in despair. These are the ones who have been truthful, and they are the righteous.