I take your point on the 23 signatures. But a previous letter to similar effect circulated with 45 names (some of them are on both letters) in late July according to NCR. I leave you to draw your own conclusions on that.

People on here, or all over the internet, can say what they like, and do. 

The point I am trying to make relates to this as a public letter, and a letter signed by people presenting themselves as experts. The letter is clearly designed to create the impression of an academic consensus, or a quorum of serious opinion on the matter - that is, the opinion of people who know the topic and should be reckoned with more seriously than, say, my opinion on supply-side economics or your opinion on quantum mechanics. I don't think this is a particularly difficult point.

If the signatories were simply asking the Pope for clarity, there was no need for an open letter. Making it an open letter is designed to draw attention to their request for clarity.