Is there a sin incurred by uncovering the face when following the opinion of some scholars who permit it, along with covering the rest of the body? And is it obligatory to denounce a woman who uncovers her face?

The disagreement among scholars regarding a woman uncovering her face when there is no fear of temptation is permissible. There is no sin upon one who is reassured by the correctness of the opinion allowing the uncovering of the face. As for condemning women who uncover their faces in front of non-mahram (definition) men, this depends on the issue of whether it is obligatory to cover the face or to lower the gaze, and on the permissibility of condemning in matters of scholarly disagreement. If it is said that it is permissible to look at a non-mahram woman without lust, then condemnation is not appropriate. However, it is permissible to offer mutual advice and to explain what one considers to be the stronger opinion.