The article made the distinction between criticism of an idea and criticism of the person behind the idea. "Of course we can and should say that ideas are mistaken, but we can’t just call the person a heretic. We need to debate the actual idea." It says right there that criticism of an idea is welcome.
Moreover, "heresy" implies that a person becomes heretic - socially despicable - by embracing an idea. This is what the author opposes. And for good reason - embracing the concept of heresy means you're only allowed to think things sanctioned by the current sociopolitical philosophy. And since every society has some amount of batshit insane ideas it believes, allowing for heresy means cutting out the safest / most peaceful way of correcting that insanity.
