[wimpycat]

Depending on how inherently intelligent the evil person is, dialogue can defeat evil, but only when your side of the dialogue is backed up by a significant, credible threat of force. But even then, you can't actually defeat evil through dialogue, only contain or draw boundaries around it.

[Chancellor Palpatine]

The Cold War is an example of your corollary.

[r9etb]

but only when your side of the dialogue is backed up by a significant, credible threat of force.

In other words, no. It is the threat of force, not the dialogue, that does the trick.

The problem with "dialogue" is that both parties have to agree on what is right and wrong. Dialogue succeeds only when one side agrees that its position is wrong, and that the other party's position is right.

But if we grant that one of the parties is "Evil," then clearly the concepts of "right and wrong" are not even in play -- to be "evil" is explicitly to defy those concepts. A dialogue based on "right and wrong" simply cannot form a valid basis for negotiation.

Successful negotiations are only possible if both sides agree to the terms. Experience shows that "evil" either rots away from the inside, or must be forced into submission. Thus, the grounds for "negotiation" are either containment (which requires the threat of force), or actual use of force.