Not at all. Calling someone a racist is a personal attack.
Not always. Calling Hitler a racist is not a personal attack as Hitler himself knows that he believes in the seperation of races. So it is with the KKK and Malan,Botha and all their pals including Terreblanch.
But saying someone is a racists who is not a racists is an insult, imagine saying Tutu or Mandela or Naude are racists, now that's a personal attack.
Some people however are racists and are hiding it knowing full well that society finds racism to be dispicable and in order to keep it hidden they will never verbally say I am racist, they will only act it out and give other reasons to their racists behaviour. Call this type of people racists will make them say you are personally attacking them and they will be really hurt, but not because you are wrong, but because you have removed their pretence of not being racist.