[pauloday]

You make a lot of excellent points but I think you might have misinterpreted my comment, because it doesn't seem like we disagree. You mention that evil cannot be defined in precise terms, and that's exactly what I'm talking about. It's not a property of things in reality that can be measured, it's a judgement about things made by people. The judgment may be very rational, but it can't be based wholly on objective reality. For that to be the case, it'd have to be based on a physical law or property rather than a moral principle, and I just don't see how that's possible. Your argument for why Hitler was evil is really solid, not because it's based in objective reality but because it's based the principle that the continued existence of the human race is a good thing. I'd say that's a solid enough principle that it may as well be objective reality. But technically speaking, it's still a subjective judgement that we're making about how things should be, rather than an objective observation of how they are.

This is a really pedantic, subtle and (I think) important distinction. If one sees good and evil as objective truth, they're reliant on the source of that truth for their moral judgement. This explains the jihadists you mention. It's not that they enjoy being murdering maniacs (although I'm sure some do), it's that their source of moral truth tells them that the infidels are evil and must be destroyed (or whatever), so they see what they're doing as a good thing.