First, let's be clear: not everyone views it as given that Trump is racist. The ability to see what you want to see, and overlook what makes you uncomfortable, is very strong. A decent person who does not pay much attention to the election may come away thinking that accusations of racism are false. Maybe we shouldn't be too ready to forgive them for their ignorance on this, but this happens to all of us to varying degrees.
Second, there are obviously times in which reluctantly going with the racist candidate is better than the alternative. Racism is not literally the worst thing in the world. If Smith says that black people are lazy and he'll work to change that, while Jones says that the way out of the Middle East is through judicious use of nuclear weapons, then I'll vote for the racist -- not because I'm okay with racism, but because it is better than the alternative at this time.
This is how some people (ignorantly) view Clinton: as an evil, selfish crook who will happily harm the nation so long as she profits. Trump, on the other hand, is despicable but not deliberately harmful and his worst policies can be prevented (they think). Therefore, despite the regrettable fact that Trump is racist, he is the better candidate.
This reasoning is wrong, I think, but it is not the same as "being okay with racism". If it is, then I'm okay with racism when I vote for Smith.