Food is also consumption. But without food people die, so this consumption directly contributes to keeping the value of the economy up by keeping the workforce alive.

As for the poo safely removing it in WWTPs also costs more money than what can be recovered in energy or hopefully phosphate in the near future. Also the capital investments are significant and as they age and need replacement this value is also gone.

However the alternative is people dying of Cholera and other shitty diseases en masse, so both the investments as well as the expenditures are well spent.