This is thing thing that is missing here:
WHAT ABOUT OUR PASS RUSH?
We were already razor-thin last year, and we lost O'Brien Schofield to free agency. Avril and Bennett played a lot of downs last year and we all saw what happened to our pass rush after Avril went down in the Superbowl. The Seahawks have brought in a lot of potential edge rushers in free agency, even kicking the tires on Greg Hardy, but so far nobody has been brought in.
So right now Irvin is our #2 edge rusher behind Avril, with no experienced depth behind him.
Sure, if he left we can move K.J. Wright back to the SAM linebacker spot, which probably suits him better then WILL, and hope that Kevin Pierre-Louis can stay healthy and continue to progress at WILL. But we also lost Malcolm Smith, so we have very little depth should KPL not pan out or KJ or BW get injured.
At any rate, another edge rusher was already a priority... if we trade Irvin it becomes a huge need. And as some have said, why trade him for a 3rd round pick and lose him for this year if we could get one more cheap year from him and then get a comparable comp pick when he signs elsewhere in free agency?
There's only one reason I can think of for why we might make this trade: We are going to sign Justin Houston to an offer sheet. It's been speculated that if any team was going to do that it would be a winning team picking low, and that it would happen after the draft so that the picks would be future picks with lower present value. Well, that time is upon us. If we signed Houston we certainly wouldn't have room to re-up Irvin. At the same time, in terms of edge rushers, we wouldn't have nearly as much need for Irvin - his value to us would be greatly decreased.
So there you have it: We're getting Justin Houston