Because I was reading one of Caleb Durward's articles (this one: http://www.channelfireball.com/articles/legacy-weapon-examining-the-banned-and-restricted-list/ ) and it got me to thinking about Jace and how he'd be in modern.
I think Caleb brings up some very valid points, especially the fact that modern is pretty much a combo-centric format with Jund being the closest thing to mainstream control (U/W shows up every now and then, but bar the rare Sun Titan deck, they're just tempo). Jace actually gives the format at the very least a win condition in a control deck bar a 6 mana Titan or a White Sun's Zenith.
Remember this is the format with turn 3 Karn, turn 3 BBE, turn 3/4 combos that win the game and no free counterspells. Tapping out for Jace really doesn't seem all that amazing in that regard, and alienating control entirely in a format honestly makes modern seem worse and worse.
Also, from my experience playing Jace in Legacy, he's not a horribly mindless card, as much as the dogmatism attached to him may suggest. Sure, Brainstorming is a free card, and played right can be a pseudo-3 cards, but you've got to actually Brainstorm right, and a lot of the time you most certainly can't be playing a 4 mana Brainstorm. Modern has a million answers to him as well, with the standard format where Jace was introduced being dominated by Bloodbraid Elf (Oh, what a coincidence). Jace seems like a perfectly unban-worthy card. Heck, Legacy has all the free counterspells you could ask for and still you'll never be dropping Jace on turn 4.
The only arguments besides "He's broken" I really see thrown around a lot are basically that he costs a fortune which isn't what WotC want for modern (Seriously, if that were the case, the entire Jund deck would be subject to being banned; I'm looking at you Tarmogoyf (a card that would probably still see more play than Jace in modern)) and that he "oppresses blue card choice". So, Jace oppresses Blue card choice? Well, so does Vendilion Clique and Snapcaster Mage; It's just not a legitimate argument. Heck, Dark Confidant oppresses Black card choice, Tarmogoyf oppresses Green card choice; You can do it for any colour.
Well, go ahead, tell me how stupid I am for believing Jace is fine.