Custom software is, to a non-hacker, the definition of "difficult to review, test, and maintain." You may as well suggest they input their data into a mystery box with some pixies inside who will crunch the numbers for them. :)
Remember, Excel (and spreadsheets in general) ARE custom software, written for this exact need, and with decades of polish and bug-fixing so that even non-wizards can use them.
I agree that we should not fly the space shuttle from an Excel macro. But I feel that suggesting economists should write software instead of use spreadsheets is not only throwing out the baby with the bathwater, but also throwing out the bathtub and the whole bathroom too. Specialty tools exist for this very use case. Let's discuss how to improve them instead of indulging our hacker instinct and reinventing a hammer every time we need to drive a nail.