I feel that better answers could be gained if the wording of the question was more along the lines of what would the Renaissance thinkers feel about slavery. There was still slavery despite the Renaissance, so the immediate answer would be that there was little effect. I do think that the humanism of the Renaissance would speak quite loud to decry the dehumanization of slavery. The power of the Renaissance resided in its ability to praise education and the general notion of individual knowledge. On face value, both of these would go against the idea of enslaving another individual. It is difficult to envision the humanism that was so stringently a part of the Renaissance would have tolerated or allowed the enslavement of another. If education was so important to the Renaissance movement, then the attempts to enslave another and deny them education would be something that humanist thinkers who played formative roles in the Renaissance would deride. The glorification of Greek and Roman ideals that was so prevalent in the Renaissance did not necessarily revere these social orders because of slavery. Hence, it would make sense that these particular thinkers would not embrace it in their own setting. Much of this is speculation because the focus of art and artistic prowess in the Renaissance composed art for its own intrinsic value and not for a larger statement about social conditions, of which the stand on slavery would have been included.