Ask any slave or anyone who doesn't own slaves what they think about the matter. Also, it is not in Man's inherent nature to be a slave to another Man. Slavery and abortion are not directly comparable questions. Trying to argue otherwise introduces a red herring argument that evades a direct answer to abortion questions and attempts to obfuscate the issue.
Legalized abortion is predicated on a similar supossed fact that an unborn child is less human.
The two issues are indeed very comparable. All slaves are undeniably living human beings with all the same parts as any other human being. No Man has the right to enslave another. This is different from the pro-choice argument. It says that they have not yet become human and don't do so until they at least reach the point of viability.