IT WAS NEVER ACCEPTABLE TO SUGGEST THAT LINCOLN MIGHT ACTUALLY HAVE BEEN AN ABOLITIONIST

There have been many reasons for this, both among politicians of that time, and historians since.

Lincoln himself had very good and sufficient reasons for concealing this fact from the electorate. Politicians seldom tell the truth if it is not in their best interests.

Douglas tried time and again to advert to this, in the debates, but it was countered, and  taken, to be merely a Douglas campaign strategy rather than a fact well known to political insiders like Douglas. 

Douglas even spelled out in the debates how the Republican Party had been formed as a more or less single issue abolitionist sectional party, but it was interpreted as campaign rhetoric, and Lincoln has since the Civil War generally been painted as having been a moderate on slavery.