Spock is logical enough that, between his support and McCoy's, Jim feels this is the right call. That doesn't mean it's any easier to listen to the dissenting opinions. That angry, grieving part of him still agrees with most of them--but he's made the decision not to act off of it.

Ultimately what he tells the crew is that they are trying to promote compassion through the universe, and if they can't do it in their own lives they have no business trying to encourage it anywhere else.

By the end of the month he even has Starfleet Command behind his idea. The hard part now will be convincing Khan.