The role of the GM

[Cybren]

On another forum someone made a thread conjecturing that unclear rules are 'unfair' to players and empower 'tyrannical' DMs to abuse their players. You can probably tell by my use of quotations that I don't share that persons opinion, but I'm curious what other people think of the idea of GMs as neutral interpreters of a 'complete' rules system rather than arbiters of rules in their own right. Something the person said to me (before getting increasingly hostile that I don't share his opinion) stuck out as just flat out wrong:

The DM's primary job is not to be a rules arbiter, but to design or manage the campaign, control the NPCs, and keep everything moving. The rules should stand on their own. Any situation that the rules don't cover is a hole in the rules. There will be some of these in any edition, since players can take infinite actions. But when literally everything anyone tries is subject to DM approval or interpretation, that's a big freaking problem.

emphasis theirs.