Looking into his biography, it seems that he was indeed pitching the engine not as a means of efficiency, but as a means of avoiding mistakes in mathematical tables. It would have done Babbage well to insist he couldn't possibly solve all classes of mistakes, but would have solved a great many of them! "Why yes Senator, you are quite intelligent and handsome and make a fair point, allow me to give you the finer picture..."

Would have also been a fair point if Babbage had channeled his inner techbro and insisted it would directly replace human calculators; simple machines like Babbage's will chug along blindly on obviously erroneous data, but humans for all their sloppiness can often backtrack on errors.