Can an observant Jew attend a wedding between a Jew and non-Jew?
An observant Jew should not attend a wedding of intermarriage. We are prohibited to give positive recognition or encouragement to an aveira. It is called chanufa, and intermarriage is definitely included in that. Intermarriage is one of the gravest things that a Jew can conceive of; it implies a tragic loss to the Jewish nation, and is something we must seek to avoid at all costs. Presence at such a wedding is a personal expression of legitimacy.