When Kofi Annan went to Syria in July to negotiate “peace” with Bashar Assad, it was a farce. Immediately after Annan left, Assad resumed slaughtering the Syrian people en masse. Annan soon resigned as UN Special Envoy, declaring that peace with Assad was impossible.

Since that visit, Assad has ordered his thugs to use SCUD missiles, cluster bombs, and other terrorist tools to kill civilians and stave off the fall of his regime. Assad clearly has no desire for peace or negotiation.

Still, Lakhdar Brahimi, the UN’s current special envoy, traveled to Syria this week to discuss peace with Assad. Brahimi declared that the situation was “worrying,” and hoped to find a “solution” to the crisis; never mind that Brahimi’s previous “solution,” a brokered ceasefire, didn’t even hold for a day.

If 40,000 people were not dead and 500,000 not displaced, it might be easy to laugh at Brahimi’s naiveté and gullibility. Unfortunately, Brahimi’s decision to meet with and legitimize Assad will likely prolong the Syrian crisis.

It is clear to any objective observer that Assad is not willing to accept a solution short of military victory. If he was, he could have done so by now – or he could have accepted asylum in a foreign nation. (This is a decision that Assad will regret when he ends up like Muammar Gaddafi and Saddam Hussein.)

Brahimi claims his visit with Assad encouraged dialogue. In reality, his visit had only one effect: to legitimize Assad as the governing representative of Syria. Instead of isolating Assad, Brahimi has done the opposite.

Symbolism matters. When the UN Special Envoy treats Assad as a legitimate leader, it makes it easier for countries such as Iran and Russia to justify their support for him. It also justifies Assad’s claim that he isn’t murdering civilians to preserve power, but that Syria is merely in a civil war.

Brahimi’s visit also plays into Assad’s delusional fantasy that his regime can survive. And it gives the Syrian Army a reason to keep fighting for him. The UN should be doing all it can to show Mr. Assad and his forces that there is no hope of winning. Instead, Brahimi’s visit has done the opposite. And this boost of confidence will very likely prolong the bloody conflict.

Brahimi’s supporters argue that a diplomat’s role is not to take sides, but to serve as a “neutral” arbitrator. But this kind of moral equivalency is bad diplomacy, and morally bankrupt to boot.

If a despot who has killed 40,000 of his own people is not evil, then who is? Brahimi claims his goal is to help Syria “get out of this crisis.” But that will only happen when Assad realizes he has no support in the international community, and no other option but to flee or be killed. The international community needs to speak with one voice, and the UN Special Envoy should be leading the charge.

Since the United Nations was created in response to World War II, it is instructive to look at the diplomatic disaster that led to that conflict. In his recent book, “In the Garden of Beasts,” Erik Larson examines the tenure of William E. Dodd, the American ambassador to Germany from 1933 to 1937.

Dodd soon came to realize that Hitler could not be reasoned or negotiated with, and urged America and other free nations to unite, take stronger action against Hitler, and isolate him in the international community.

The American diplomatic elite of the time ridiculed Dodd for this approach. They actively sought to undermine him, claiming, like Brahimi, that an effective diplomat should engage with a dictator, no matter how unpleasant. They believed that talking to and negotiating with a despot was the only way to achieve peace.

Dodd, of course, knew the Nazis had no interest in peace; that there was no moral equivalency in diplomacy; and that if he didn’t actively oppose what was happening in Germany, he was for it.

So Dodd, on his own, undertook symbolic gestures to oppose the Nazis, such as boycotting party rallies and shunning German leaders with blood on their hands. This partly led to his removal from the post in 1937. But history would prove Dodd prescient. And perhaps if the rest of the world had followed his approach to diplomacy, Hitler would have felt more constrained or faced active resistance earlier.

Symbolism and morality matter in diplomacy. Without them, a diplomat is not only ineffective, but also enables dictators and despots. Mr. Brahimi should vow never again to see Mr. Assad – unless it’s on foreign soil or at Assad’s funeral.