Paul Pillar makes  the case against taking either side in the Saudi-Iranian rivalry:
It would be just as much of a mistake for the United States to tilt in favor of Iran in this conflict as it is to tilt in favor of Saudi Arabia. Taking either side in this rivalry, as with many other international rivalries, entails several disadvantages for the United States.
There is a strong bias against neutrality in our foreign policy debates. Not taking sides in this or that conflict is rarely taken seriously as an appropriate response. Instead of asking whether the U.S. should even take a side, it is taken for granted that the U.S. “must” choose one or the other, and the main debate concerns only how much and what kind of support to provide. This is a recurring problem in debating the proper response to conflicts inside countries as well as rivalries between them. One reason for this is that U.S. interests and the interests of another state or faction within a state are conflated from the beginning, and this is done to make it much more difficult to recognize that the U.S. doesn’t actually have interests in the conflict or rivalry in question. Hawks often “adopt” a faction or government and then fault the U.S. for “failing” to do enough to help “our” side. Refusing to take a side is portrayed as “abdication” of “leadership” or otherwise pilloried as too passive, and the bias in favor of action in our debates helps to make it harder to advocate against taking sides.
Today’s Fareed Zakaria column  shows how difficult it is for most pundits to do this. Even when arguing for steering clear of regional sectarian rivalry, Zakaria can’t avoid endorsing U.S. support for the Saudis:
In general, the United States should support Saudi Arabia in resisting Iran’s encroachments in the region, but it should not take sides in the broader sectarian struggle.
But it is not possible to support an overtly sectarian Saudi government in its preoccupation with opposing Iranian influence without being pulled into the “broader sectarian struggle,” in no small part because the Saudis define their resistance to Iran’s supposed “encroachments” in terms of religious sect. The Saudis falsely claim that their war on Yemen is aimed at “resisting Iran’s encroachments,” and the U.S. has been supporting their campaign from the start, and in so doing it is helping to fuel sectarian hatreds in Yemen and beyond. Zakaria correctly recognizes the pitfalls of being pulled into sectarian conflicts in the region, but won’t acknowledge that the U.S. is caught up in them because of the support it provides to sectarian governments. He specifically mentions the growing sectarianism in Yemen, but doesn’t make the connection with U.S. support for the Saudi-led intervention there. Despite explicitly saying that the U.S. shouldn’t take sides in “someone else’s civil war,” he approves of doing just that by accepting that the U.S. should keep supporting the Saudis.
One of the most common arguments for siding with the Saudis in their hostility towards Iran is that they are our “ally,” and therefore the U.S. should automatically support the position of its “ally.” This overlooks that the U.S. has no treaty obligations to the kingdom, and ignores that the so-called “ally” does virtually nothing for us. The U.S. cannot expect and does not receive the sort of automatic support and cooperation from so-called “allies” that many hawks expect the U.S. to provide to them, but it is often assumed that the U.S. would be “abandoning” the so-called “ally” if it chose not to take their side against a regional rival. For some reason, many Americans forget that the relationship with an “ally” exists to advance our interests and not so that our government can indulge theirs in its vendettas and obsessions. When U.S. interests are no longer served by such a relationship (if they ever were), the U.S. doesn’t need and shouldn’t want to keep it the way it is.