Slavery and abortion resemble one another only in that they are moral issues to some people and not to others.
Lincoln made slavery a moral issue, as did the Abolitionists of his day, while claiming to be not an Abolitionist (I think for tactical reasons, to avoid a label he might have deserved).
Whereas modern abortion opponents do indeed oppose abortion on strictly moral grounds, much as the Israelites condemned Jezebel for her institution of a tophet (a sacrifice of children) in the holy city of Jerusalem, it will continue to mystify historians whether the secretive Lincoln was in fact a moralist, or even a deist. Some suspect he was neither, and that his use of the slavery issue (and its "cure", civil war) was pragmatic and drily instrumental, and that his real motive in argument -- his motive -- was to implement the American System of Henry Clay, a strictly economic agenda that needed some sort of left-handed way of being implemented in the agrarian United States of his day.
In other words, the Civil War may have been all about instituting high tariffs and subsidies for manufacturers and better business conditions, and subsidies, for railroads -- remember, Lincoln was a railroad and patent lawyer.
It might all have been about the money, and all the rest, window dressing for a dark victory of the money power.