What is the ruling on one who holds that publicizing a sin out of pride in it is considered a major sin and not an act of disbelief that expels one from the faith, contrary to the saying of Sheikh Ibn Uthaymeen that whoever boasts about fornication should be asked to repent or else be killed, because it implies his deeming fornication lawful?

The difference between committing a sin openly (publicly) and considering it permissible (halal (definition)): Not everyone who commits a sin openly considers it permissible. Many of those who commit sins openly still believe in their prohibition. Although this is dangerous, it does not render the perpetrator a disbeliever. Ibn Uthaymeen clarified that a person who commits a sin openly does not become a disbeliever by doing so, unless their sin is an act of disbelief itself. The principle among Ahl al-Sunnah (definition) wal-Jama'ah is not to declare someone a disbeliever due to sins unless those sins constitute disbelief. Ibn Uthaymeen differentiated between one who commits a sin openly out of heedlessness and one who does so boastfully and recklessly, showing disregard for the Creator's greatness. The latter is in a worse state, and their boastfulness and recklessness may indicate that they consider the sin permissible. Disregarding God's greatness and turning away from His rulings are considered types of disbelief.