His appeal to James is quite ironic, given the high Christology of James. As Blomberg and Kamell note, in their comment on Jas 2:1:
The last genitive, “of glory” can be taken in two different ways…The second, appropriate in such a strongly Christological context, is appositional, so that Christ is equated with the shekinah glory of God, the “localized presence of Yahweh.”
As Robert Sloan observes, the term “has a long prehistory in Jewish history and theology as a euphemism for Yahweh,” building on the light in the tabernacle (Ex 40:34) and temple (1 Ki 8:11) and Ezekiel’s vision of the heavenly throne (Eze 1:28), it is widely used throughout the NT in close association with God and Christ to refer to their presence, and in this context it is not occurring “by itself,” but with a triad of related titles.
James (Zondervan 2008), 106-07.
This is diametrically opposed to Tuggy’s “humanitarian unitarianism.” Therefore, James wouldn’t regard Tuggy as a fellow Christian (or “brother”). To the contrary, he’d view Tuggy as a Christ-denier. Unitarianism slanders the person of Christ. He'd do well to think less highly of himself, and think more highly of Christ.