“But Rad introduces standards…
“But Rad introduces standards of fictional discourse against my objection that ‘praying to God’ is factive.”
I don’t think the connection between “writing letters to Santa Claus” (to take the example) and standards of fictional discourse is quite so straightforward. The language-game surrounding Santa Claus (to take one example) is complicated by the fact that parents engage in fictional discourse that children are expected to treat as factual discourse about Santa Claus, for a few years of their life at least. A number of kids who might tell you that what they are doing is writing a letter to Santa Claus, wouldn’t be saying it under an implicit fictional-that operator. You could, of course, just dig in and insist “Well, in that sense they aren’t writing letters to Santa Claus. They just think they are, and you’re only inclined to call it a letter to Santa Claus when you slip into the fictional context by playing along with the child’s false beliefs.” And I’d agree with you that there’s a sense of “write to” (and “speak to,” “pray to,” and other forms of direct address) where the second person has to exist for you to count as having done it. What I’m more doubtful of is the idea that this is the only sense in which the terms can be used in direct discourse. I’d be interested to know why you think direct (non-fictional) uses of these phrases presupposes the existence of the indirect object.
I’d also note, in this connection, that it’s a common use of English to say things like: “People pray to many different gods,” without presupposing that all of the gods that people pray to exist.