Well, Martin Luther King, Jr., was a racist only if he knowingly accepted disproven beliefs about the differences between the races; and he did. Hence, he was a racist. In fact, he'd still be a racist if he was alive today. Since he rarely changed his beliefs.
What type of argument is this extended argument's second sub-argument?
Consider the following extended argument:
Hypothetical Syllogism
Categorical Syllogism
Argument by Elimination
Argument Based on Mathematics
Inductive Generalization
Predictive Argument
Causal Argument
Argument by Analogy