Debate defends assumptions as truth. Dialogue causes introspection on one's own position. Debate causes critique of the other position. Dialogue opens the possibility of reaching a better solution than any of the original solutions. Debate defends one's own positions as the best solution and excludes other solutions.
Debate creates a closed-minded attitude, a determination to be right.
In dialogue, one submits one's best thinking, knowing that other people's reflections will help improve it rather than destroy it. In debate, one submits one's best thinking and defends it against challenge to show that it is right. Dialogue calls for temporarily suspending one's beliefs. Debate calls for investing wholeheartedly in one's beliefs. In dialogue, one searches for basic agreements.