I think the main reason metal is in opposition to Christianity and Christian values is because unlike many pagan religions, Christianity emphasizes forgiveness. Not just forgiveness among people, but forgiveness of corporations for ruining the environment, forgiveness for the man who burned your home to ground, forgiveness for the doctor who was too drunk to save you sister when she got in a car wreck, etc.
All this forgiveness is unnatural and retards the growth of a person because it encourages him to exist in a bubble where everything is happy and no one is wrong unless they don't love and follow your God. As a Christian, you start forgiving people (and yourself) of preventable failings that, if dealt with correctly, would lead to them (or you) becoming a better person.
Christianity also set up the notion that your spiritual growth and worth could be measured by your material wealth (this concept gained the most strength in America). If you owned less actual property than your neighbor, then it must have meant that God wasn't watching over you as diligently as him, so there must have been something wrong with you.
But you KNOW you're not the 'sinner' (another horrible concept) in your house, so your thoughts turn to your wife or Daughters. After all, God tells you that they are the more sinful of the sexes, so the 'sin' must lie with them. You can see how this might lead to domestic abuse as well as the greed-driven small-mindedness we see today.
As for the opposition to Judaism, there's a page I read that talks about how Judaism holds a very virulent hatred for everything that stands in its way. This hatred is so consuming that Jews seek to destroy everything that is not like them in any way possible. This includes conversion, war, subversion and a whole list of other activities. That only seems to account for some of the hostility that black metal, which is very jealous and protective of its own historical identity, shows for this religion.
(I think that page was out of Nietzsche, but I haven't found it again so I'm not sure.)