Since we are refining the thread to being guests at a religious ceremony, I don't think the the sanctity of the event is the issue. The real issue is that you are a guest, and as a guest, have an obligation to play by your hosts rules. This applies even if the activity is not "sacred". If you don't like the rules, then don't go.
If a sacred event plays out in a public square then a "no photography" request is somewhat moot. Most sacred events, however, occur inside buildings or on private (or at least non-public) land. In these cases, no photographs should be taken. There are exceptions, such as situations where harmful illegal activity is part of the ceremony such as human sacrifice, child abuse, ceremonial rape, or animal cruelty.