Spock's argument that the natives have chosen a system that appears to work for them has a few obvious flaws:
Did the natives make a choice? They do not understand the true nature of Vaal, so despite being practically immortal they must not have been present when it was constructed. It was therefore at best their ancestors who made the choices that led to their current society, not them.
Do they have a choice now? Vaal is very quick to enforce its rule when a potential threat like the Enterprise landing party appears. Akuta at one point warns other natives that they are practically calling down lightning on themselves for doing acts that Vaal forbids (kissing). It seems likely therefore that any native who choses not to conform to Vaal's will is killed.
Spock's argument that the natives have chosen a system that appears to work for them has a few obvious flaws:
Did the natives make a choice? They do not understand the true nature of Vaal, so despite being practically immortal they must not have been present when it was constructed. It was therefore at best their ancestors who made the choices that led to their current society, not them.
Do they have a choice now? Vaal is very quick to enforce its rule when a potential threat like the Enterprise landing party appears. Akuta at one point warns other natives that they are practically calling down lightning on themselves for doing acts that Vaal forbids (kissing). It seems likely therefore that any native who choses not to conform to Vaal's will is killed.