The ancient classic “Antigone” is rich with moral quandary, as the titular character nobly faces the prospect of death to do what she believes is right: honoring her brother with a proper burial. But as Adil Mansoor deftly observes in his one-man show “Amm(i)gone,” now playing at Woolly Mammoth, the why behind that decision is just as important as whether you’d make the same choice. He’d bury his brother — and so would his mother. But they’d do it for different reasons, she as an act of care for a loved one, and he out of an abstract sense of social justice.