Why is it that sabotaging the Bright Brotherhood's rockets personally at the navigation terminal lowers your karma, but talking Chris into doing it and then providing him with the means to do so doesn't? If killing the Brotherhood is morally wrong (and, let's be clear, it is), shouldn't it be wrong regardless of how you go about accomplishing it?

Karma is a meaningless statistic that provides nothing of value to the player. It's best to just ignore it entirely.

Also, killing the Brotherhood is not morally wrong. It's morally grey. It's wrong if you support that particular raider tribe, it's good if you support pretty much anyone else that doesn't want to be harassed over technology.

The Bright Brotherhood, not the Brotherhood of Steel. (Although, if you'd like to discuss the morality of slaying the BoS en masse, I'll just point out that the Hidden Valley bunker is home to a considerable number of children and most moral systems consider it wrong to blow up children.)

And karma affects the slides you get in the epilogue, so it's not meaningless.