If there is a tribal marker, it's not MWI persay; it's choosing an interpretation of QM on grounds of explanatory parsimony. Eliezer clearly believed that MWI is the only interpretation of QM that qualifies on such grounds. However, such a belief is quite simply misguided; it ignores several other formulations, including e.g. relational quantum mechanics, the ensemble interpretation, the transactional interpretation, etc. that are also remarkable for their overall parsimony. Someone who advocated for one of these other approaches would be just as recognizable as a member of the rationalist 'tribe'.