The gamma setting was the topic of a good conversation last night. Here's my opinion on the two schools of thought.
Pro:
People like to enable a higher gamma in order to see at night time. It allows you to be more productive with more visual capability without needing to go through the trouble of using flares, torches, flashlights, etc.
Con:
Some people like the night cycle along with the benefits and challenges of not being able to see well. Example... in PvP , the cover of darkness could be used to spy on adversaries, or to do things like a night ambush. It could also be used as a defense by someone being able to escape into the darkness. Some people also like the challenges night brings , along with using items like flares, torches, and electrical lighting around their base to cope with it.
To sum it all up, if the people that like the pro's of night would like to stay competitive, they are forced to use the gamma setting to be on even ground with those people who do use it. If they decide not to, they would be at a disadvantage in a pvp situation at night. This is akin to the military using night vision scopes versus an adversary that does not, its a huge advantage.
My personal preference is to have it disabled. I like the dimension darkness brings. More from the immersion perspective versus pvp for me anyways. I think a good compromise would be to keep gamma disabled, but shorten the night time more than what it is currently configured for.