You literally use slavery - where human beings were the victim of prejudice and legal discrimination to the extent of being denied personhood - as an excuse to deny personhood, promote prejudice, and have legal discrimination against the unborn.
Slavery was wrong because innocent human beings were reduced to the property of others... and you want human beings to be reduced to the property of others.
You pro-aborts are as rotten as promoters of slavery could ever be, but don't literally copy the position of the slavers and pretend you're somehow the opposite - that's beyond disgusting.