my grandmother, who lived through the depression on some tiny dirt farm in georgia likes me, but she says I’m a “tightwad”.

This genuinely hurts to hear.

the psychological trauma of being poor for years has made it so I simply can’t stomach the risk of being a “good consumer”, let alone buying into something truly insane like a stock bet. gambling is just insane to me, I don’t care if there’s a “system”… the entire affair seems like it would be agonizing until it was over.

The "system" collapses if not enough people invest and consume. That's why this maladaptive behavior is encouraged to the point of being considered normal.