Larian isn't done implementing network stuff, so just starting a game with different network options may not be the only reason there are singleplayer and multiplayer buttons.
That would actually be worse. If the setting actually becomes important.. if there is a permanent change to the game based on a decision made at the point of beginning a new game.. then you really are going to have new players making critical mistakes and/or running to the forum asking for clarification before ever playing the game.
Since multiplayer will always be drop-in/drop-out, if singleplayer were to ever truly lock you into a "permanently singleplayer" game, anyone would be a fool to ever choose it. To choose singleplayer at that point would be to basically say
"I can see the future and know beyond a shadow of a doubt that I will *never* want to temporarily make this game co-op, ever, even temporarily. Not for any reason. At all. So sayeth my magic 8-ball.".
Only a fool would do that when the multiplayer choice would always provide them with the ongoing option to play alone or with friends. The multiplayer option IS singleplayer. It is also multiplayer. It is both modes and always will be because co-op is designed to be drop-in/drop-out. There is no such thing as a multiplayer game that can not be played singleplayer. And there is also no such thing as a singleplayer game that can not be played multiplayer. And that's why the option is redundant, and also why making the choice meaningful would actually backfire and make the singleplayer setting a foolish trap.
