Killing is wrong, I decided a while back, not just because of the negative utility experienced by humans prior to their death because of the killing ritual, but because any human killed is effectively robbed of the positive utility they would have had after death, along with their consent being violated. In this case by the way it IS meaningful consent, as suffering, or at least loss of positive utility, will occur. Therefore, the Doomsday Button is probably immoral to push, as it essentially kills everyone on Earth.
EDIT: Look in the comments section. Thanks to Bazompora, who corrected me on this one, I now believe you CANNOT be robbed of positive utility, simply because the act of being robbed implies deprivation, which implies that the 'owner' had a right to their future utility - which is absurd, because owning one's future would have hilarious consequences (sort of). Anything can change one's future utility, so you can't say that the dog crapping on the street robbed you of 10 more years of life, even if you would have live 10 more years had it not set in motions a chain of events because of that.
You must before doing something like this consider that the vast majority of humans on this world want to be alive, and have a right to choose whether to live or die as they see fit (see this, especially the end). Therefore the Doomsday button is wrong because you a breaking a fundamental moral right, so says moral intuition. But is being robbed of positive utility really such a crime?
Moral intuition, again, says yes. If you slander someone and stop them from getting a highly-paid job that would have raised their positive utility compared to their state otherwise, you have quite obviously done a bad thing. So the Doomsday button is doubly wrong, sadly.
But can you just say, for the greater good, since more lives of suffering will not have been made? No, because morality does not take into account the greater good, it takes into account a harm, and a harm is something you cannot do if you do not wish to violate your morality, which people generally do not seek to do for feelings of guilt. For the purposes of this discussion, breaking of consent, violation of rights and loss of positive utility most likely constitute harms.
I'm a little rusty in my morality arguments, but reading over things I might get a bit better. If I can be bothered. In any case, until next time.