Metaphysical facts are fundamentally unknowable anyway--if you could determine them through some type of experiment, they'd be physical facts. There might be some metaphysical facts you can prove by argument, but I doubt it.

You could even argue that metaphysical statements are meaningless, though you run into problems going too far that way as well.

Metaphysical statements are indeed meaningless if you can't determine them through some type of experiment. That being said, the fundamental laws of our universe could also be considered as metaphysical statements since they "describe the physical", the precise definition of "metaphysical". However, those metaphysical statements can be determined through experiments and that's why they're "useful".

@philwelch: I quoted you here http://syskall.com/why-we-should-eradicate-agnosticism-from-..., hope you don't mind. I tried contacting you by e-mail but it didn't work.