You have to look at the whole picture than just quote Lincoln's famous speech doesn't mean he was a racist.
He challenged Douglas for a US senate seat. Lincoln's famous view was "no extension of slavery". Douglas' view indicates that slavery could exist in any state where it had a majority support. The national press loved it because Douglas was so prominent. He had already introduced Popular Sovereignty which was the basis for the admission of Kansas. He was also well known throughout the country. Lincoln had the chance to speak for the New Republican party with... again "no extension of slavery". The debates were inflammatory. It was well known Lincoln had a squeaky tenor voice. You have to remember that Douglas was called "the little giant" because he had a deep voice. Douglas was a tremendous speaker. They traveled through state of Illinois and Lincoln kept saying "no further extension of slavery".
Now, The Mason-Dixon line runs through bottom half of Illinois, separating Southerners from Northerners- While the first debates went on "no further extension of slavery", they went to a place called Charleston, Illinois south of Mason-Dixon line (a very conservative area). When Lincoln got there, in 4th debate, he gave a 'white supremacy speech'- kinda of sleazy speech for people in the South. That is Lincoln's same quote you posted. Believe it or not, it was shocking, considering Lincoln's career. A moral laps in a sleazy attempt to get votes. It was a bad moment in his life- This was such as abnormal exception to his speeches and total moral opposite to his life. Because, through northern part of Illinois he continued with "no... extension of slavery".
Slavery is morally wrong- In the Declaration of Independence it states "men are created equal". Douglas would say- This country was created by white man, and the Declaration of Independence doesn't apply to black, or native Americans or any others- we're taking about all white men are created equal. People should be able to decided for or against slavery- slave or free. Lincoln would say- we either have American Ideals or we don't.