The phrase "singing praises of" normally refers to praising someone or something. Antonyms of this phrase would be to criticize, condemn, disapprove, or belittle. When we criticize, we point out flaws or weaknesses that someone or something possesses, while condemning means to express strong disapproval towards them. Disapproval means to have an unfavorable opinion or a negative evaluation of something or someone, whereas belittling refers to making someone or something seem unimportant. The antonyms of "singing praises of" paint a different picture, where there is a negative tone of speech instead of the positive one of admiration.