Alternative terms could be a craze, a fad or a fashion. These terms also suggest that the activities in question are being imitated. 

There's nothing wrong with calling some group activity a cargo cult. The term is meant to be pejorative as it signals the speaker or writer's attitude towards it and this is a signifying act that is part of the meaning of the term. 

In that sense, the terms fad or craze are the closest synonyms, in that they cannot be interpreted other than pejoratively, whilst fashion can be either way, depending on the writer or speaker's intentions signalled in the rest of the sentence or piece of text.