[2] Rothstein has been called one of Denmark's top researchers in new religious movements,[3] and has been credited with making them a topic of scholarship.
[1] Another area of scholarly interest is indigenous religions; he was the first researcher to describe the Penan people of Borneo.
[4][5] He has called Lars Hedegaard "an assailant" (Danish: en voldsmand), leading to criticism from other free speech advocates.
[6] He has been described in a Christian periodical as "uncompromising [and] a wonderful, intelligent man who is both warm, caring and generous with praise for both colleagues and students"[1] and by another commentator in the same publication as demonstrating "one-sided bile" and "hatred" in his utterances concerning Christianity.
[8] Among books he has written or co-edited are: Belief Transformations: Some Aspects of the Relation between Science and Religion in Transcendental Meditation (TM) and the International Society for Krishna Consciousness (ISKCON) (1996), Secular Theories on Religion: Current Perspectives (2000) (co-author with Tim Jensen), New Age Religion and Globalization (2002),[9][10] New Religions in a Postmodern World (2003) (co-editor with Reender Kranenborg) and The Cambridge Companion to New Religious Movements (2012) (co-editor with Olav Hammer).