One of the five fundamental pillars of conservative thought, as phrased by wikipedia (which is itself merely paraphrasing Russel Kirk, a foundational of post-war American conservativatism), is:

> A conviction that society requires orders and classes that emphasize natural distinctions.

Racism and bigotry are not errant additions to conservatism, they're a logical extension of one of its foundational pillars. (Though that is not to say that the left is not without its racism and bigotry as well, it's just less of a natural fit)