One of the hoariest arguments about international diplomacy is that talk is a reward and that talking with another government somehow validates, supports or endorses the other regime. This outlook misrepresents the very purpose of the tool of diplomacy, which is not to bestow rewards but instead to advance the interests of the state wielding the tool. To forgo use of the tool doesn’t put anyone else in his place; it only handicaps the statecraft of the government that doesn’t fully use the tool. The argument nonetheless gets heard a lot in the United States, partly because it is so easy to move from the greatness that Americans associate with their own country to the idea that merely getting a conversation with U.S. representatives constitutes a prize and an expression of favor. The argument also is a way of bashing whatever administration currently has responsibility for conducting U.S. diplomacy.
The Israeli analyst Meir Javedanfar and Matthew Duss of the Center for American Progress have a perceptive piece on what the diplomatic tool has accomplished regarding a state toward which the talk-as-reward often gets applied: Iran. They describe what talk or the mere willingness to talk has helped to achieve, even assuming the worst about Iranian intentions and even without any agreements being reached with the Iranian regime. A U.S. willingness to negotiate demonstrates that it is not the impediment to a better relationship. It has been instrumental in getting other powers, especially Russia and China, to cooperate further in imposing sanctions on Iran. It has had similar salutary effects inside Iran, in demonstrating that it is the Iranian regime that stands in the way of a better relationship with the West. And it has enhanced the credibility of what the United States says about Iran.
I would add some other advantages of talking with any troublesome regime (which, of course, is what the United States did with the Soviet Union throughout the Cold War). Not preemptively forgoing diplomacy because of worst-case assumptions about the other side's intentions opens up opportunities if the assumptions turn out to be not altogether true. The diplomacy increases the negotiating space and permits the striking of deals that range over multiple issues. And talking to the other side reduces the chance of incidents and misunderstandings spinning out of control.
Of course, if one wants an incident to spin out of control because one is hankering for a war, that would be a reason not to talk. We know that George W. Bush thought along those lines when he talked with Tony Blair about how the United States might provoke an incident that could be the excuse for launching what became the Iraq War.