> Software was always marketed (and discussed with normal people) as something that could automate error-prone tasks, thereby eliminating the inevitable mistakes humans make when performing those tasks.

That's far from a community touting that computers don’t make mistakes.

> Would Excel be the cornerstone of so many businesses if it sometimes gave the wrong value as a sum of a column?

You mean like if it was running on a Pentium with the FDIV bug? :)

I agree there's a perception computer output is generally reliable, and that leaves users at the mercy of snake oil parrots that are generally unreliable and are sold without a warning. But I don't agree the cause is that touting.