This a simile. This is because a simile uses like or as to compare two things. A metaphor doesn't use like or as, but it still compares things.
Calpurnia says that people are not going to change since she is "talkin' right, they must need to learn themselves, and when they would prefer not to realize there's no other viable option for you yet keep your mouth close or talk their dialect."
Calpurnia says one ought not to tell each of the one knows, right off the bat since it is not genteel and also on the grounds that people don't care to be around the individuals who know more than they do.
