If you don't stand for something, you'll fall for anything
This phrase is not exactly an idiom but it's an often used strand of thought which traces it's roots back to early 1900s use, right before the Great Depression, and was also used during the days of WW2.... It's been resurrected again in popular culture via the country western artist Aaron Tippin.
To discover more interesting ideas about this particular phrase, please see the link provided.
https://quoteinvestigator.com/2014/02/18/stand-fall/