From your link:
The fact is, Lincoln said almost nothing about race. He was not that interested in race…Race was not a major intellectual construct for Lincoln…And the 1858 speech was purely defensive. That doesn’t excuse it, but he was being attacked in those debates as believing in negro equality.
I think the fact that he was defending himself from attacks by his opponent in the US Senate race that he was to "liberal" in his views regarding negro equality says a lot. That one quote was bad, but in the context of the debate, he was trying to convince the idiots that he wasn't to liberal. He failed and lost to the bigger racist.
Everyone must be viewed within the context of their time. Lincoln was the more liberal candidate in the race that he lost and he was wise enough to allow his views to evolve over the next few years.