Religious doctrine is not the primary determinative factor for human action.
Okay, having made that clear, I feel better already.
The Buddhist exceptionalism in question is the modernist image of Buddhism as the exception to a general tendency of religions to be violent. The motivation for trying to formulate some coherent thoughts on this came during a discussion at a dinner party where good friends asked me to “justify” (I think they meant explain) Buddhist violence in Myanmar against the Rohingya.
The corrosive effects of that exceptionalism is that once shown as an artifice, a pretense, an empty claim of superiority, Buddhism generally becomes degraded. Just as when—confronted by historical issues such as slavery and the slaughter of Native Americans, and contemporary issues such as institutional racism and increasing income inequality (along with a hundred other ills our society is heir to)—American exceptionalism becomes corrosive of America generally, including those values worth upholding.
When asked by my friends about the violence in Myanmar, I made some to my memory unsatisfactory comments regarding the role of religious nationalism, and the problematic character of thinking that belief determines action, and the corollary that since religious beliefs claim ultimacy, they should be the ultimate determinants of action.
Much more adequately, Dan Arnold and Alicia Turner provide an understanding of the situation in their essay “Why are we surprised when Buddhists are violent?” (New York Times, Monday 5 March 2018, here). It is well worth reading.