Those of us who believe that students should use calculators only after understanding the calculations themselves have to fight that well-worn battle of "let the calculator do the drudgery, teach the kids to interpret what the calculator is telling them." There are many levels of rebuttal to that silliness, the weakest being, "What do you do when the batteries die/the power goes out?" No one, not even the person raising that argument, really thinks it's a good one. There are plenty, though, for whom the concept of the necessity of "numeracy" is so clear and obvious that they've never thought through a clear and obvious rebuttal to the siren song of universal calculator usage.
I'm currently skimming through my personally-annotated copy of Sherman Stein's amazing book Strength In Numbers and came upon this beautifully-worded, succinct reasoning:
There is also the risk that a computer may play the role of the autocratic teacher who says, "Don't ask why. Just do it the way I say." It is then a mysterious black box, and using it places the pupils in a position of dependency. This circumstance is most unfortunate in mathematics, where pupils should develop self-confidence and accept nothing on faith. Several teachers have told me that "the capacity to reason seems to get lost when you start pressing keys too early."I refer to calculators in class as "devil boxes", and I talk to my students about "black box numbers". It seems I'd absorbed Stein's lessons well, even though I'd forgotten this particular passage from a book I last read several years ago.
By the by, I've met Professor Stein. He's signed two books for me (Strength In Numbers and How The Other Half Thinks) and gave me an algebra book he co-authored in 1969. His "popular audience" books are extremely interesting and well written, and the algebra book is among the best I've ever seen, certainly better than any book adopted in California in the sixteen years I've been teaching.
I used to recommend John Allen Paulos' book Innumeracy to people who ask me to recommend one "popular audience" math book; now, if I can recommend only one it's Strength In Numbers.