I really feel for any GM who even dares to attempt to run a game in the modern world. There is a whole Library of Congress of information detailing that world......
Imagine, a GM that knows little about chicago, or dislikes undeclared aspects of it, or just wants to make it their own city by way of major changes, running a campaign in chicago.....
Player "Let's go to the top of the Sears Tower, we maybe able to see from there!"
GM "You get to the top and find your view blocked by a taller building."
Player "WTF?!?!?!"
Or something less offensive...
Player "I head to the nearest Portillos, I love their hot dogs"
GM "Portillos? Umm what's that?"
Player "Ummm a famous chicago restraunt?"
GM "That was taken over by McDonalds, and its now called McPortillos."
Player "Eh???"
Or
Player "Let's call Mayor Daley, he'll help us bust these drug dealers!"
GM "Well that ruins this adventure, whatever shall I do now...." "Umm he doesn't answer his phone"
Player "Well let's call Police Chief Weis!"
GM "No answer"
Player "Attorney General Madigan!?!"
GM "Died"
Player "Roland Burris?!?!"
GM "He answers, and wants money to help you..."
One of the significant benefits of a setting is that it allows everyone playing the setting a chance to come to the table with knowledge of the setting. This allows them to play characters that LIVE within the setting, rather than characters that experience one as it unfolds before them. While some players and GMs do not seek or some may not even desire this game play, you must accept without reservation that there are players that DO like this aspect of playing in a detailed setting. This doesn't intrinsically make the player BETTER, nor does it make the player WORSE.
It is what the player does with this information, that makes them a good or bad player. Believing that it is the setting that causes this problem is a failure in identifying the problem.... which isn't always the player with all this wealth of knowledge.
Now for an example on par with one of the stories of these "realms lawyers" that I found most annoying, as it shows a CLEAR example of a bad PLAYER, not a bad SETTING.
Back to chicago.....
Player "We're heading to Rosemont, and breaking into 410 McKinley St! The man that lives there is a mafia enforcer! We'll get him to talk!"
GM "WTF??! Who??"
Player "Tommy Two guns, he lives there. I read it in the Chicago Tribune yesterday!"
GM "No such person lives there"
Player "Yes he does, and you're a crappy GM, that just can't handle that I know more than you about Chicago!!!", goes buck wild..... storms the house anyway.... and promptly dies from a airliner that lands short at O'hare
Damn glad there aren't any RPGs played in the modern world. What to do with all the powerful figures that could so easily solve the players problems, and the endless amount of information about the world?
/sarcasm off
Yet somehow, we manage.... right?
A GM shouldn't have to know a setting down to the nitty gritty details, but they should be familiar with it via broad strokes of a paint brush. If a GM wants to remove Sears Tower from their Chicago, expect a player to be all "WTF??" and have an answer other than "GM Fiat"
Anyhow, if you have someone that knows a setting in more detail than you as the GM, use communication, communication, communication.... You could USE that player to enhance the game, if you care to try. Will that player shine a little brighter than the other players that know nothing? Most likely, but again... USE that player. Ask that player to help you create a player guide for the other players. During this creation, the two of you should come to a better understanding of just how close to the original setting you are wanting to run it, and you may learn more about the setting.
If this fails, again it isn't the setting that created this beast, it their mother and father.
The days of GM IS GOD and IT IS THE GM's GAME, should be placed in the past. Everyone at that table is contributing their time, energy and creativity to the game. It is everyone's game.
If you just don't like the setting, fine, whatever..... find a way to move on.