Weren’t there a few episodes where they discussed losing their principles if their material conditions deteriorated?

Yep, once on DS9 when they get stuck in the 21st century and they're in the sanctuary district/ghetto:

BASHIR: But it makes you wonder, doesn't it? Are humans really any different than Cardassians or Romulans? If push comes to shove, if something disastrous happens to the Federation, if we are frightened enough, or desperate enough, how would we react? Would we stay true to our ideals or would we just stay up here, right back where we started?