Douglas and the Democrats was making a charge that Lincoln and the Republicans not only wanted to get rid of slavery but full emancipation and intermarriage. It was a racist taunt. At the time only 15% of the North could be classified as abolitionists and not all of them wanted 100% full equality and intermarriage, so all politicians, even those proclaiming equality. Even Thaddeus Stevens who was in a relationship with Lydia Smith (mixed race) didn't publicly acknowledge that or advocate for full equality.
For an objective view of Lincoln there is no better commentator than Fredrick Douglass and his address in 1876 is one of the greatest either by Douglass or about Lincoln and the entire speech is worthy, but relevant to your point Douglass says:
http://teachingamericanhistory.org/library/index.asp?documentprint=39
I have said that President Lincoln was a white man, and shared the prejudices common to his countrymen towards the colored race. Looking back to his times and to the condition of his country, we are compelled to admit that this unfriendly feeling on his part may be safely set down as one element of his wonderful success in organizing the loyal American people for the tremendous conflict before them, and bringing them safely through that conflict. His great mission was to accomplish two things: first, to save his country from dismemberment and ruin; and, second, to free his country from the great crime of slavery. To do one or the other, or both, he must have the earnest sympathy and the powerful cooperation of his loyal fellow-countrymen. Without this primary and essential condition to success his efforts must have been vain and utterly fruitless. Had he put the abolition of slavery before the salvation of the Union, he would have inevitably driven from him a powerful class of the American people and rendered resistance to rebellion impossible. Viewed from the genuine abolition ground, Mr. Lincoln seemed tardy, cold, dull, and indifferent; but measuring him by the sentiment of his country, a sentiment he was bound as a statesman to consult, he was swift, zealous, radical, and determined.
And then there is Lincoln as a person. While some northerners advocated equality as a principle, for Lincoln it was part of his personality. Again Douglass relates his first meeting with Lincoln:
http://www.mrlincolnandfreedom.org/inside.asp?ID=69&subjectID=4
Long lines of care were already deeply written on Mr. Lincoln's brow, and his strong face, full of earnestness, lighted up as soon as my name was mentioned. As I approached and was introduced to him, he rose and extended his hand, and bade me welcome. I at once felt myself in the present of an honest man — on whom I could love, honor and trust without reserve or doubt.
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