There are several synonyms for the phrase "unknowing foolishness". One common term is "ignorant stupidity", which refers to a lack of knowledge or understanding leading to foolish actions or decisions. Another possible synonym is "naive idiocy", which suggests a combination of innocence and lack of common sense leading to foolish actions. "Unthinking folly" is another option, indicating a lack of foresight or consideration leading to foolish choices. Other possible synonyms include "foolish ignorance", "clueless idiocy", and "unintelligent recklessness". Ultimately, all of these synonyms highlight the idea of foolishness resulting from a lack of awareness, understanding, or forethought.