I dislike racism and any dehumanization or removal of the importance of the individual. I do not like group-think or those who seek to control or oppress to further their own means.
Consider that DD knows the vast majority of people don't like him because of what he stands for. Consider that he understands endorsing someone does them damage because of this. Then consider if it's possible he has ulterior motives. Trump has said on camera that he denounces DD. R Spencer also says he supports him (& is aware the majority of people who know of him strongly dislike him), & he wants "national socialism" in addition to racial division. That is the opposite of what Trump's economics are. The fact that people think Trump is racist increases racial division by pitting half the country against the other half (one half accuses, the other half accuses back) and increases the chances for socialism & racial division; which is what their goals are.
Think about it like this, the entire premise of this thread is to defend a man who has a racist past by saying he is capable of change; therefore his association or endorsement by certain people shouldn't tarnish their names. Perhaps this is true, there is no way to know what was truly in the man's heart. When he filibustered the Civil Rights act for 14 hours straight (the longest ever from what i have read); that was over a decade after he became "disinterested" in the KKK. However he lived many decades after that and could very well have changed. Young people tend to make mistakes & get carried away easily. This is one reason forgiveness is important.
This same standard needs to be applied to everyone; if you accept that one person can change, then you shouldn't hold the past of someone you don't like against them if they demonstrate change; or dismiss it by saying they aren't genuine (because you don't like them).
It is my belief from all my observations; most Americans detest racism. There are some individuals who are racist; but they are few & far between. I am using the classical definition for racism here, hating or thinking lesser of some1 because of their race.
the modern interpretation dilutes it's gravitas by equating it to stereotyping. I'm not saying stereotyping is good, i think anything that causes people to stop looking at each other as individuals has potential to cause harm.
my 2 cents