Well you should care if you want to be hired, published, or generally taken seriously in certain environments. (Note that speaking "proper" English is not alway

Well you should care if you want to be hired, published, or generally taken seriously in certain environments. (Note that speaking "proper" English is not always what you want either; there are some social situations where other dialects will get you farther -- and, of course, all of this also applies to languages other than English.) But I also take your point. The problem--as is often the case with various forms of stereotyping--is that such preconceptions are simultaneously useful as indicators about a person you are dealing with (such as level of education), but also deserving of serious skepticism since they can have the effect of disadvantaging certain groups, cause you to miss interesting opportunities, and generally making life less interesting by enforcing a stultifying uniformity.