Aside from the moral obligation to help others:
(1) Without Al-Anon's constant re-sensitisation to the problem, I develop the same blind spot with alcoholics that alcoholics have with alcohol. I start to act out without realising it. Self-neglect, self-justification, control, guilt, (s)mothering, excuse-making, rescuer-seeking, and blame. Naaat cooot.
(2) Alcoholics, whether drunk or sober, will remain alcoholics, and, without Al-Anon, I get real cranky with them.