The reference I posted (I think the only actual grammar book listed in the thread) explicitly has it in the list of subordinators.
That should have said “reflexive acceptance.”
Also, I should clarify, that’s a diagnosis I’m offering. I’m not characterizing the actual arguments given. I’m trying to explain why people would offer these arguments, when these arguments are so blatantly flawed. The motivation must be somewhere other than in the rational force of the arguments themselves–they have none. My hypothesis is the plausible one that we are witnessing the work of the “No Initial Coordinators” ‘zombie rule’*.
*I probably picked that phrase up from Language Log somewhere. It’s a rule that no actual expert or authority espouses, but which still gets taught to grade schoolers, so it remains alive in much of the public’s consciousness.
Right, but that’s a really old source.
Nothing very contemporary calls “for” a subordinating conjunction.
And it’s not one. It doesn’t behave like one. A subordinating conjunction’s associated clause can be moved around inside the sentence. “For” doesn’t work that way.
Grammatically, “For” behaves like “And” and “But,” not like “Because” and “Even though.”
Your source even blatantly runs against this problem in one of its exercise sets. It says for each word on the list of subordinate coordinators, the reader should construct a sentence using that coordinator in the middle of the sentence, and using the same phrases but moving the coordinator to the beginning. So, for example:
“I walked to town because I’d run out of gas.”
and
“Because I’d run out of gas, I walked to town.”
Well, “for” is on the list. But it turns out to be impossible to comply.
“I walked to town, for I’d run out of gas.”
*“For I’d run out of gas, I walked to town.”
For want of a nail, the shoe was lost.
For want of a shoe, the horse was lost.
For want of a horse, the rider was lost.
For want of a rider, the battle was lost.
For want of a battle, the kingdom was lost.
And all for the want of a horseshoe nail.
That’s the prepositional use of “for,” not the conjunctional use.
Well…
Thanks for many of your suggestions concerning the quiz. As noted, at least one, possibly two changes will be made as a result.
But no thanks for the completey wrongheaded and blatantly, demonstrably incorrect criticisms some of you offered concerning the conjunctional use of “for”.
FWIW students are for the most part now getting grades of 90 or above on quizzes like this one, so the subject now seems to have been officially taught. 
Also, I diagrammed some of the long initial coordinator ‘for’ sentences discussed in this thread. God, it brings back memories. Sentence diagramming, even if it is based on dubious linguistic claims, is fun. Wish I had a camera here–I’d show you the diagrams if I could.
For is a coordinator, not a subordinator. And the word ‘for’ in its coordinating sense does head the main clause of each of the examples I discussed, scifisam’s protestations to the contrary. I recommend you not answer grammar questions anymore, scifi. You don’t analyize complicated sentences correctly–not even by the standards you yourself espouse. And these weren’t subtle errors, either.