On Monday, War on the Rocks hosted an open letter signed by a number of former senior U.S. policymakers that strongly promotes the quick ratification of Montenegro’s accession to NATO. With the exception of Russian opposition, Montenegro is a relatively uncontroversial candidate for membership. Yet when considered more broadly, the signatories’ arguments raise troubling questions about NATO’s purpose, mission, and approach to future expansion. Is NATO a tool for spreading democracy, a reward for societies that seek greater ties with the West, or is its primary function still as a defense alliance? These are not new questions. Yet in an era where NATO members are increasingly concerned about its defensive mission, the signatories’ unquestioning endorsement of further expansion is both unfortunate and misleading.

With a tiny population, an insignificant military, and few security threats to speak of, Montenegro would seem to be the perfect case for proponents of NATO expansion. Certainly, it will not contribute to NATO’s security mission in anything other than symbolic terms. It has only 2,080 men under arms, and a military almost entirely focused on internal security concerns. And while it is true, as the signatories note, that Montenegro contributes troops to NATO operations in Afghanistan, they neglect to mention that there are only 17 of them. On the other hand, Montenegro is also unlikely to add substantially to NATO’s security burdens. It neither shares a border with Russia, nor has a substantial ethnic Russian population as problem-cases Georgia and Ukraine do. As a result, there is unlikely to be major opposition to Montenegro’s membership here in Washington.

Yet Montenegro’s military insignificance belies the importance being attached to it as a test case for further NATO expansion. For starters, by focusing on Montenegro’s reforms and “strong commitment to Euro-Atlantic integration” as a reason for membership, the signatories make an implicit argument that any country which meets nominal membership requirements – typically military and democratic reforms, as well as the absence of territorial disputes – will be permitted to join. They highlight the importance of Montenegro’s accession as proof that no third-party state can veto NATO membership decisions. As NATO Secretary General Jens Stoltenberg put: “Montenegro’s membership will demonstrate to all those who aspire to membership that if a country delivers, so does NATO. Our door remains open.”

Unfortunately, this interpretation of the open door policy is skewed. We can all agree that Russia should not have a veto on NATO expansion (though policymakers would be wise to take Russian security concerns into account more often). But this has too often been interpreted to mean that Russian opposition is itself a reason to support a country’s NATO membership. In fact, the 1995 Study on NATO Enlargement was clear that expansion should not occur unless it strengthens the alliance’s effectiveness and preserves the political and military capacity to provide for the common defense. It seems doubtful that Montenegro meets this standard. It is certain that other prospective members like Ukraine or Georgia do not. Admitting such states merely to defy Russia — or as Evelyn Farkas, one of the letter’s signatories put it, “standing strong in the face of Russian intimidation” — is akin to cutting off our nose to spite our face.

In fact, for all the talk about Montenegro’s commitment to Euro-Atlantic integration, there is a surprising amount of ambivalence within the country itself about NATO membership. The government has made reforms and joined European sanctions on Russia, but disagreements within the ruling coalition required it to undergo a vote of confidence as recently as December. Public opinion has been mixed, with fewer than 50 percent of Montenegrins supporting NATO membership, and strong opposition from the Russian-aligned Orthodox Church. Another article in these pages blamed such popular ambivalence on Russian-owned media. Yet it is the height of arrogance to suggest that Montenegrins are not every bit as able as Western publics to resist Russian propaganda and form their own opinions. Meanwhile, the state is extremely poor (per capita GDP is only $6,373), and corruption remains a problem.

Even Montenegro’s relative poverty seems not to be a problem for the letter’s signatories, who quote Vice President Joe Biden’s agreement that integration into Euro-Atlantic institutions will contribute to stability and prosperity in the region. In doing so, the letter implicitly endorses the long-standing argument that NATO membership is a first step towards membership of the European Union and rapid economic development. But as the European Union’s 2015 report on the topic illustrated, Montenegro is at best moderately prepared to join, with further progress required. And economic ties are a poor reason for the expansion of a defense alliance. Likewise, the signatories’ argument that Montenegrin membership in NATO is necessary to maintain stability of the Balkans is flawed. In the more than ten years since NATO ended its Balkan peacekeeping mission, no country in the region has returned to conflict.

The problem underlying all of these arguments is the continued lack of a clarity in NATO’s mission. This is certainly not a new problem: The organization’s post-Cold War activities were often little more than a March of Dimes-style attempt to reinvent itself, eventually morphing it into an organization designed to spread Western values. Yet as Russian aggression in Eastern Europe has grown, the alliance has reverted to its original focus on defensive issues. The result has been substantial tension between these goals. Today, NATO’s open door policy is actively detrimental to its security. Indeed, there would be little concern about NATO’s ability to defend itself in the absence of its earlier expansion into the Baltics. Montenegro’s membership indicates an intention to continue with expansion, worsening relations with Russia, and opening the door to future conflicts in Eastern Europe.

States must be free to choose their own destiny. Yet if we are to accept that argument, we must accept that it applies equally to existing NATO members, who retain their ability to veto further expansion if it is detrimental to their own security. On its own merits, Montenegro’s membership in NATO is relatively uncontroversial. It will neither enhance, nor substantially detract from the alliance’s security. Yet in arguing for Montenegro’s accession on largely symbolic grounds, the signatories of the open letter raise larger concerns about the future of NATO. When the U.S. Senate addresses the issue of ratification, its members would be well–served to ask these broader questions. Does NATO promote the common defense of existing members, or seek to expand the Euro-Atlantic democratic community? It cannot accomplish both.

Emma Ashford is a Research Fellow in Defense and Foreign Policy Studies at the Cato Institute. Follow her on Twitter: @emmamashford.