Hmmm. I suppose a case could be made that the clergyperson is acting as an agent of the state in contravention of the SOCAS standards. However, I’m much more inclined to read it in the same context as getting a fishing license or getting mail delivered.
The state might contract with a chain of outdoor-recrreation stores to sell fishing licenses. It’s convenient for the fishermen; you can obtain tackle and your license at the same place. It’s convenient for the state; they don’t have to hire additional clerks in the Department of Managing the Environment (whatever it’s called in that state) to issue licenses for money. And it’s convenient for the stores, because they attract business by offering the service and probably made a small proportion of the license fee.
But it does not constitute an endorsement by the state of that chain of stores; it’s merely a public-private partnership for mutual benefit.
Likewise, the U.S.P.S. can contract with a given trucking company to carry loads of mail from one SCF to another, or with Joe Retiredguy to deliver the mail along a rural route. Those contracts are not endorsements of the company or of Joe; they’re employing the services of a private entity to fill a governmental need.
Similarly I can in some states sign my will before witnesses who aver by their signatures that it’s me, I told them it’s my will, and I signed it before them, or I can have it notarized under the same process. Does that mean the state considers a notary’s word to be as good as that of two or three other people? Or does it mean that they’ve picked one class of people on the basis of special training to do the job.
In the U.S., the state recognizes marriages solemnized before specific categories of people, such as judges, who are equipped by their training to ensure that it’s a legal marriage and that the people are competently taking the vows involved. Since a large number of Americans practice a religion in which marriage is a vow before God, employing the services of a clergyperson who will be witnessing those vows before God as also the person who can solemnize a marriage in the eyes of the state is a convenience to the state, not an endorsement of their faith.
There would be nothing stopping me from recruiting a Rabbi to witness my marriage (other than the fact I’m already married) – despite the fact I’m not Jewish. And I could always snag a magistrate for the same purpose. As it happens, I’m Episcopalian, and would have my wedding in my home church.
The same range of choices, with the same preferences, are available to any American of whatever belief (including the null set of atheism).