TL;DR: People are bigots because it makes them feel better, not because they can't reason.
The REASON it is so important to separate these concepts. Is because. One of the ways bigots get people hauled off to camps, is to conflate mental illness / disability with wickedness in the mind of the public.
Because THEN people get more scared of someone with a developmental disability than of someone who is a "dapper" Nazi.
And then guess who suffers and is killed.