I don't think I've met anyone who didn't have some sort of prejudice against others. For example, Lou Dobbs and Bill O'Reilly won't shut up about immigration, drugs, and the "dangers of Mexicans and illegal aliens".
Is Lou Dobbs racist? Probably. Nevertheless, the degree of racism may not reach a threshold that would alone dissuade me from voting for him. If he decided to do immoral things based on his prejudice, then I would rule out Lou Dobbs. Same with Bill O'Reilly, except, I suspect I'd ruled out Bill O'Reilly the first time I saw him on TV.
I watched several interviews of Ron Paul, some from before the time he considered the presidency. I've never heard him say anything racist. In fact, he claims we are inappropriately using illegal immigration as a scapegoat for our economic troubles. (You'd think he would blame Mexicans like everyone else).
In a book he wrote in 1987 he speaks ill of racism along with other behaviors he considers repugnant or harmful to society. Racism in the United States has only received due attention in the last 40-50 years. In context, it would not surprise me if older people (anybody currently over 40 years of age) were raised in environments where such ignorant attitudes or behavior were considered acceptable.
Just look at the portrayal of people in movies released in the 70s and 80s.
If conclusive evidence showed that Ron Paul held racist attitudes then, but changed, this would be acceptable to me (if not commendable) given Ron Paul's emphasis on civil liberties and his current view of the world.
There is no conclusive evidence. I do think the Ron Paul campaign should do more to dispel the allegations or claim responsibility (depending on the veracity of the allegations).
An ignorant attitude is not a crime. Otherwise most people would be in jail at some time or another. I think someone with a potentially questionable attitude on race might be better for the world than someone who intends to start wars of aggression.
I also think that someone who is racist would have trouble being diplomatic with Cuba or Venezuela.
http://www.ron-paul.for-president.us/ron-paul-a-diamond-in-the-rough.html
http://thespinfactor.com/thetruth/2007/12/10/ron-paul-at-the-spanish-debate/
At the same time, while Ron Paul might (allegedly) have a racist attitude, he is not promoting racist legislation. On the other hand, Hillary Clinton and Obama are, despite their likely good intentions.
Does the alleged taint bother me? Sure, but I don't subscribe to racist ideology. I oppose it, and that's why I like so many of Ron Paul's views and policies, such treating people as individuals, friendship with our "enemies" (Iran, Venezuela, Cuba). He also opposes laws on victimless crimes that statistically affect "minorities" and believes we should treat drug users as individuals who may need help, not criminals to be punished.