-It kills the battery life....but you can turn it off.
-It makes the 3DS more expensive..but it only costs $169 as it is.
-It's not needed...but when its used well, it's a sight to behold (Starfox, Zelda).
Plus it's used in Nintendo Video, various 3D websites accessible via the browser, and hopefully 3D movie rentals/Netflix in the future.
People went apeshit when they saw the glasses free 3D in the palm of their hands at E3 last year. There's a push for 3D in smartphones, as we speak. 3D is here to stay. It's an asset for the 3DS, not a liability *. And even for the select few that have a problem with it, they can just turn it off (and what I think will become standard, MGS3 will actually turn the 3D off automatically whenever a player uses the gyroscope to control someting.). I joked about a 2D 3DS a while back but I don't think that, even in these crazy Nintendo times, it will become a reality.
*edit* Bolded/Underlined for Rol :P
