My theory is that debating, especially formally, follows certain formats that make most everything you say pretty predictable in terms of rhetorical function and segregated from real feeling. Similar to how acting usually is easier for stutterers. Informal conversation for me is quicksilver and unpredictable and more based off of feelings somehow. So maybe stuttering is caused in some measure by a hesitancy to trust and embrace one’s feelings, or perhaps by an impulse to hide one’s feelings from oneself.