"???Do the arithmetic that matters and donít get bogged down in arithmetic that does not amount to a hill of beans."

Indeed.  I agree completely.

Considering the cost of production alone does not amount to a hill of beans.  You say it yourself  when you catalog the side effects of "[building] hundreds of new coal-fired plants."  Fossil fuels have side effects.

If your back of the envelope accounting included the Total Cost of Production, including long-range economic impact of the side effects of these fossil fuels, the relative cost of hydrogen produced by electrolysis would look much more favorable.

Do the arithmetic that matters.  Do all of it, not just the half that supports your position. 

You may need a bigger envelope.