What is the Shar'i ruling on refusing to deliver a wedding invitation due to the presence of forbidden acts (munkarat) therein, and is the one who refuses considered an extremist?

Assisting and guiding towards sins is forbidden, based on the Almighty's saying: "And do not cooperate in sin and aggression," and the Prophet's (peace be upon him) saying: "Whoever calls to misguidance will bear a burden of sin equivalent to the sins of those who follow him." Therefore, refraining from helping in such matters is not an act of strictness, but rather an obligation. Furthermore, jurists are of the opinion that one of the excuses for not attending a feast is the presence of an objectionable act (munkar) therein, and attendance is not obligatory if they are not confident in their ability to change the objectionable act, especially if the objectionable act involves musical instruments and free mixing (of genders).