The biggest problem with calculators (rather than slide rules), was that because calculations with big numbers (large mantissa) were so easy, people got used to doing them that way without consideration.

Using a slide rule meant inherently knowing order-of-magnitude, rounding, and precision. Once calculators make it easy they enable both new kinds of solutions and new kinds of errors (that you have to separately teach to avoid).

At the same time, I basically agree. Humans are very bad calculators and we've needed tools (abacus) for millennia.