The problem is that people don't understand enough to apply the equations. I use paper and pencil (or whiteboard which amounts to the same thing) all the time. In real problems, the actual equations need to be derived from given information and the rules of algebra.

Any student who actually understands algebra can easily use the calculator correctly. The problem is that people - all people DO - make mistakes and LOTS of them. This is why one needs to know if an answer makes general sense.