Christopher,
Consider the following question: Why Superman doesn't need a boss?
Because he has super vision.
I think mathematics is a language similar to English or any other natural language in many aspects. Now, if you allow me to extend the analogy as far as I like I think the problem your students are having is similar to the problem some students learning English have when they encounter homophones or to understand the double meaning that is common in jokes.
Of course someone might think as nonsense the claim " I smell a rose." if it is unaware that there is a flower with that name and only is used to hear that word in the context of something moving upwardly in the past (the past of rise). Failing to understand the multiplicity of meanings doesn't allow to make sense.
I don't think your students are wrong but that they are similar to a kid that demand an explanation of how come the same string of letters have different meanings or someone asking us to explain a joke. As you pointed out ":"The meaning even of 2 2 was a problem. Not when it occurred by itself, but when it occurred in some situation where the two 2's are used in different ways."
This different meaning of the word are related to different contexts and uses of the number two. As a teacher you are aware the delicate and difficult task to convey this to your students. I am in no way an expert and probably only pedagogical research can help you to learn new techniques how to be more effective to show the different contexts in where different uses of mathematical symbols are used. Saying that I would be happy to hear about the specific situation your ninth grades regard as nonsense.
Regarding doing math by memorizing without thinking I would say I have a divided opinion. I think is not healthy if it extinguishes curiosity for more complex subjects or problems. But at the same time knowing thing by heart are useful and not necessarily bad if we are aware of the efficiency they have in our life. Perhaps a ninth grade wont be able to give a proof of why she should received $1 dollar change for a $9 dollar toy if she is paying with a $10 dollar bill. But, certainly, knowing that would be very useful, even if she only knows it by heart.
I have read the essay you suggested and I would leave a comment there when I have more time.
Finally, don't worry about ruining my life or career. Discussion is important and I always welcome it. As Wittgenstein said "A philosopher who is not taking part in discussions is like a boxer who never goes into the ring."