Arryn,
I don't think Johan was saying that wife-beating was right, or logical, just that the demonstration that it's wrong or illogical depends on accepting a big set of other principles, like "human life has inherent value" and "men and women have equal worth as people". If you start from assumptions like "all people are sinners waiting for redemption", "women are more sinful then men", "it is men's duty to 'correct' women", then wife-beating (under certain circumstances) is logical, the same way many people would consider it logical to spank their kids if they were playing with fire.
This doesn't say that either one is "right", tho.
Religions are perfectly capable of making predictions: "All the faithful go to paradise after they die." Have you ever seen a priest burning in Hell?
What's considered proof (at least as far as scientists worry about it) depends not only on making predictions, but making ones that can be disproven. And usually disproven in particular ways. If somebody says "I am the messiah because God came to me in a dream and said so", well, there's no way we can check that. Even if he says "As proof of my divinity, the sun will rise tomorrow", we'd say "While we can test that, it was also true that the sun rose before you became the Messiah, so what does that have to do with anything?" Now, if he says, "As proof, the sun won't rise tomorrow, because my god will cast Utterdark overnight." now that we'd be much more interested in.