Probably not the burnt parts. It probably doesn’t need explanation, but there’s some health science to why avoiding blackened food parts makes sense. The body doesn’t like the burnt parts. It has negative effects.
So what happens when you put something in 400 degree temperatures for minutes-hours at a time? Does it catch on fire? Usually not. Does it get black? Perhaps not as well. But a change does occur including the creation of acrylamide which has been established as a carcinogen enough so that even in Starbucks there are signs that say their food contains this chemical (a cooking by-product, not an additive). When foods get browned, that browning is the formation of acrylamide (among other new formed chemicals).