Liebniz' argument lacks finesse, but it's actually pretty sophisticated. Possible worlds is a pretty tricky concept to do anything with, and imagining God picking among all the worlds he could create is a pretty strong leap of imagination.
Sophistication, I would argue, does not itself impute logical coherence. In fact, it oftentimes does nothing more than obfuscate.
I know this thread train has derailed waaaaay of its original tracks but, if you'll indulge me, I'll explain.
Leibniz' argument is fraught with logical contradictions, if not outright fallacies. Firstly, it seems (to me) that most of his arguments were based on
a priori assertions, most of which based on what I feel to be his rather question-begging, recursive take on
"The Principle of Sufficient Reason." As I'm sure you know (you're a bit smarter than me in this area), he believed God to be a
necessary being without which the universe could not have come into existence or continue to exist; Leibniz' concept of God as "cosmic optimizer." However, there aren't really such things as
necessary beings, so he's already failed right out of the gate, imo. As
Sean Carroll puts it:
If you have God intervening in the world, you can judge it by science and it’s not a very good theory. If on the other hand God is completely separate from the universe, what’s the point? But if God is a necessary being, certainly existing but not necessarily poking into the operation of the world, you can have your theological cake without it being stolen by scientific party-crashers, if I may mix a metaphor. The problem is, there are no necessary beings. There is only what exists, and we should be open to all the possibilities.
Also, his BPW's idea is itself contradictory to the idea of free will* (I think it was Russell who pointed that out? Maybe others, I can't recall) not to mention his 3-omni God being self-contradictory.**
So, like Pascal's full explanation of his "Wager," Leibniz' BPW argument sacrifices logical soundness (and coherency, to be honest) for sophistication. That's my take on it, anyway. YMMV.
*As I touched on up-thread, the mainstream Christian theological concept of God giving man "free will" is incompatible with the notion of God deterministically creating a "best possible world" (i.e. "everything happening according to His plan").
**An omnipotent being would be able to create another being who is completely free and independent. Complete freedom implies freedom of thought, as well, and that one's thoughts are his/her own and accessible to no one else. Such a creation (and the ability to create it) is incompatible with omniscience (knows everything and knows everyone's thoughts). The two are mutually exclusive.
