...because western economies are built upon larger young generations paying smaller old generations for the privilege of participation; take away its buttressing and that "stable" economic pyramid becomes a rickety tower...
...you can prop up the generational productivity deficit with industrial automation to some extent, but only if the benefits of automation are democratised rather than hegemonised, otherwise a smaller-and-smaller oligarchy instead dominates an increasingly-marginalised peasantry until the whole thing comes crashing down...
...when life becomes cheap, it will be spent cheaply...
...roll back before fascism and take a look at feudalism to see how ugly things can get in a steady-state oligarch civilisation...