People:   "If God, then why bad?"[0]
  Leibniz:  "God and bad can coexist. E.g. we live in the best possible world."[1]
  Voltaire: "Here's a depiction of some fictional bad."

I don't think Voltaire engaged meaningfully with Leibniz's argument. (I think that Leibniz is simply right tho, in the mathematical sense, so there isn't much room for Voltaire anyway.)

[0] : https://en.wikipedia.org/wiki/Problem_of_evil

[1] : https://en.wikipedia.org/wiki/Best_of_all_possible_worlds

I suspect that "being right in the mathematical sense" is the very thing that Voltaire was lampooning.

Doesn't Leibniz's argument assume a single all-powerful god, and an external notion of good and evil? I would call it a 'not-even-wrong' argument - perhaps it's perfectly correct given its assumptions, but the assumptions aren't (necessarily) anything to do with this world...

We've come a long way in those 266 years: global population 10x'd, meanwhile the share of the population living in extreme poverty went from over 80% to nearly 8%, so not all optimism was misguided. Also there's a lot of room between despair and a Panglossian caricature, and I don't think acknowledging that a lot of good has happened in the past (and not necessarily suggesting it was all inevitable or automatic) rises to that caricature.

I don’t really see how you got there from what they actually said.