I recently doubted commercial viability of point-to-point Earth flights on BFR (on /r/spacex) and got lots of comments that since Musk promised it then of cours

I recently doubted commercial viability of point-to-point Earth flights on BFR (on /r/spacex) and got lots of comments that since Musk promised it then of course it would be viable and as cheap as business class ticket now, maybe twice more. The calculation that followed was, quote "200000$ for fuel price divided by number of passengers and then add 5000$ per ticket for operational expenses, total 8000$ per ticket". I wonder what sane person could believe that, even with the stellar record of SpaceX RnD.