  Sidgwick took disagreement seriously, and thought that if there was significant disagreement about the truth of some apparently self-evident moral proposition, then that casts doubt on whether that proposition really is self-evident. Intuitionists could defend themselves from this objection by downplaying the amount of moral disagreement. They might claim that a lot of moral disagreement stems from disagreement about non-moral facts, such as what the consequences of a certain act will be. For instance, two people might disagree about whether it is permissible to boil lobsters alive just because they disagree about whether lobsters can feel pain. Since the basis of their moral disagreement is this disagreement about the relevant neurological fact, if they agreed on this non-moral fact, we could expect them to agree about the permissibility of boiling lobsters alive.