I agree with you. Maybe Graham is imprecise when he blames "identity."

Is the issue really just partisanship, rather than identity as a whole? "People can never have a fruitful argument about something that's part of their identity. By definition they're partisan." 

Example: What's the difference between someone who identifies as a "health nut" and someone who identifies as a "keto advocate." The health nut has incorporated an area of interest into their identity; the keto advocate has chosen a tribe.