I'm not talking about the general mahalach in chinuch. This is a specific area of emuna.
a: The area of chinuch in emuna may need much improvement and effort, but emuna is not a simple Q&A session and whatever issue there are cannot be rectified through asking a few questions.
b. Overwhelmingly, today's kids are not primarily going off due to complex philosophical issues.
We can go on all night. The status quo of talk of emunah being shunned and legitimate questioners told to keep quiet was definitely an issue.
We're not talking about kids going off because off unanswered deep philosophical questions - more just the basic belief that permeated Jewish homes. I have nothing to do with the AMF but just now taking a look at their site - they aren't targeting kids to stop them from going off. They are addressing kids who may be frum their whole lives and go through the motions but not really believing in what they are doing.
And yes if a kid doesn't believe in what they are doing there is a much smaller chance that they will be interested in being frum other than not wanting to be ostracized. Once they get over that it's all over.
There are 2 ends of the spectrum. 1) Not talking about emunah at all 2)Talking about it a lot and bringing up discussion
There is a middle ground between the 2 which is where I think most people would feel most comfortable. The way it looks to me AMF is swinging toward #2 to distance from #1 and the letter is trying to steer it back to the middle ground.