It seemed that this subject has been studied before, or at least the title Identity Fusion was defined in 2009, although in a different context than our regular identity management topics.
The abstract of the article by William B. Swann, Jr, D. Conor Seyle, Ángel Gómez J. Francisco Morales and Carmen Huici states:
The authors propose that when people become fused with a group, their personal and social identities become functionally equivalent. Two hypotheses follow from this proposition. First, activating either personal or social identities of fused persons should increase their willingness to endorse extreme behaviors on behalf of the group. Second, because personal as well as social identities support group-related behaviors of fused persons, the 2 forms of identity may combine synergistically, fostering exceptionally high levels of extreme behavior. Support for these hypotheses came from 5 preliminary studies and 3 experiments. In particular, fused persons were more willing to fight or die for the group than nonfused persons, especially when their personal or social identities had been activated. The authors conclude that among fused persons, both the personal and social self may energize and direct grouprelated behavior. Implications for related theoretical approaches and for conceptualizing the relationship
between personal identities, social identities, and group processes are discussed.
Here is the link to the full article.