That depends on what you mean by slur. If you just mean "bad word" then we can certainly replace some, but I am not convinced saying "John is feeble-minded" rather than "John is an idiot" is really different, although saying "John has a learning disability" may be more correct (and does offer the chance that is can either be worked around or fixed).

The world "nigger" is essentially completely banned from society, so much so that people call it the n-word, but has that changed attitudes? Or is the person just going to say racist stuff with African-American instead of Nigger?