Solidarity, if it is identical to social justice or perhaps benevolence, pertains to the will, while identity pertains to the intellect. The exercise of solidarity is dependent upon how one's identity, which is admittedly "subjective," in that people can identify themselves in various ways and think that each way of determining their identity is correct relative to the moral agent. But in answer to the question of "Who am I?" in relation to moral reasoning, we should look not at what is relatively insignificant (what are our pastimes or "interests" are), but firstly the role we play in creation [our function, narrowly conceived]. This role is tied to our understanding of our family (including lineage), relations with friends and associates, community, and people.
I remember someone else in the PhD program writing her dissertation on role-centered morality, but from more of an "analytic" perspective--I don't know if she is trying to turn her dissertation into a book (or if she's still in academics). If roles are so important, why didn't the medievals talk about them? Because their moral theology already presupposes an understanding of roles and related precepts (see Aquinas's discussion of the virtues related to justice and the order of charity)--there wasn't a need to write an explicit account of roles and duties. (As Fr. Cessario once said in class, "The medievals didn't have to talk about community; they lived it.") This understanding of roles is covered, implicity if not explicitly (at least not as far as I remember) in Dr. Fleming's The Morality of Everyday Life (a review here).
For us Americans, the acquisition of a "role-centered" morality is necessary for a deepening of our understanding of the lay vocation.