David Berreby's book "Us and Them: The Science of Identity"[1] pretty much agrees with you, and makes the case that the less rich/diverse someone's identity is (in essence: the more "single-issue" they are), the more likely they are to have a narrow view of it and to cling to it regardless of its validity.

His conclusion is that an individual should cultivate multiple identities, so that each one is enriched by the others and becomes more nuanced in the process.

[1] https://www.amazon.com/Us-Them-Identity-David-Berreby/dp/022...