Well as far as I understand things, the option to turn off the lighting effects (ie, the darkness) is there for performance reasons for those that need it. An option to just remove only the flashlight probably wouldn't change much in that regard.
I can't say I'd be up for playing the game entirely in the dark myself. Sounds a bit masochistic. But I had actually thought about how it could be cool to include the light and dark in some degree of minor stealth gameplay. The zombies are plants afterall, that like light, so it would be interesting if you occasionally found sluggish half asleep ones that wouldn't attack or notice you as long as you moved slowly and didn't shine a light on them or cause any other commotion. So you'd get moments where you might want to turn your torch off and try to sneak past, at the risk of not being able to see other dangers very well. (And a fun panic moment if you wake them all up whilst right in the middle of it all)
Obviously the game is just hitting release already and likely a bit late for things like that, but might be a fun thought for the sequel. : )
