Oakland is stupid. Palmer may not be the greatest qb ever, but he's a veteran and there are probably half a dozen teams who would sign him in a heartbeat.
This, my friend, is no reason to keep a player who is old (-der) with a salary that is taking up so much of the cap as his was. The Raiders did try to keep him, but at a more cap friendly salary.
Palmer has thrown 30 interceptions while with the Raiders, against only 35 touchdowns. Many of those interceptions came not because of a an offensive lineman's screw-up, but from just plain bad judgement.
As presently constructed, the Raiders' margin for error could not, and will not, accommodate Carson's negative proclivities.
In other words, he wasn't the quarterback for us, though he may be fine for a team with at least one great receiver.
No, the stupid move would have been to keep Palmer, especially at the same salary.