People in this thread are doing an awful lot of projecting what they would do or what they think is logical. But at this point, the proposal on the table (trading for Carr) cannot be ruled out on those factors. Someone on the draft board conjectured that if Oakland cleans house this offseason, firing the coach and GM (a very distinct possibility), the new coach/GM might want to go get their guy rather than go with Carr, and they will be in the position to do it. Maybe they will, maybe they won't, but it's a possibility that can't be ruled out at this time. Whether or not we think it makes sense to stick with Carr is irrelevant to the discussion, it's what the coaching staff and front office that is in place in Oakland next spring thinks about it and what they plan to do.
I saw this same thing leading up to the trade that netted the Redskins RGIII and us a bunch of draft picks. So many people said the most we would ever get was one extra first round pick from the deal. They didn't consider the makeup of Daniel Snyder, who has an almost pathological need for winning the offseason and for making a big splash. A friend of mine and I discussed this before the trade went down and both of us agreed that if nothing else, Snyder would drive up the price of our #2 pick by making a huge offer based on his makeup ... and sure enough he did.
Logically, if I were making the decisions in Oakland, I'd keep Carr and try to build around him. But I'm not, and there is at this time no guarantee that whoever is making such decisions for them will think this way.