The phrase "cast a slur on" implies an act of defamation, insult, or prejudicial remark. There are several antonyms that can be used to counter such negative expressions, such as "praise," "commend," "applaud," and "exalt." By using these antonyms, one can shift the perspective towards a more positive and constructive conversation. Such positive expressions can help build relationships, foster collaborative efforts, and promote a healthy and inclusive environment. It is crucial to choose one's words carefully and mindfully, as words have the power to either heal or hurt.