I'll take the first bite.

Serenity Prayer by Reinhold Niebuhr

God, grant me the serenity to accept the things I cannot change, courage to change the things I can, and wisdom to know the difference.

Yes, but the Serenity Prayer is more geared towards AA and NA members... Hmm...

"... what purpose can Stoic apatheia or indifference serve nowadays?..."

Discernment. It is one of the hallmarks of maturity and wisdom. Think, "Pick your battles."

A Stoic is indifferent to what's not in his/her control. You're not indifferent to whether you live or how you live to the extent that's in your control.

Yes, but the Serenity Prayer is more geared towards AA and NA members... Hmm... — Shawn

The serenity prayer is a very good match for the stoic spirit. I don't know how far this is true but it's claimed christianity & stoicism have some elements in common, the latter influencing the former. Nietzsche was probably critiquing stoicism in christianity, he must've interpreted it as defeatism, only the weak are like that - the set of things they can change is the null set. Nietzsche'swill to power makes sense now - stoics must be eradicated and stoicisim buried for good.

That the stoic attitude is suited for addicts proves the point, doesn't it?, that Zeno's (of Citium) philosophy is about control, the lack thereof to be precise. It speaks volumes regarding how life was back then - the 3rd century BC was likely a time when "people had very little autonomy."

Intriguingly, there's a paradox lurking at the very foundation of the stoic way of life. Thus the quotes around, "people had very little autonomy". The stoic call to accept instead of resist one's circumstances makes sense also if people did have high levels of control over their lives. Isn't that precisely what "...can't be changed" - other people?!