I've summarized several comments left on the item and put together a few responses.
Ian 202128 blamed receiver Golden Tate and the Seahawks' pass protection for Jackson's issues against Minnesota in the second preseason game. He thought coaches were asking Jackson to strike farther downfield, nearly impossible given the protection. He also thought Whitehurst repeatedly had extended periods to throw.
Mike Sando: The Seahawks were definitely more enterprising with Jackson to start the game. They opened with Jackson in the shotgun with an empty backfield. Jackson found Tate for what should have been a first down. Tate dropped the ball. Jackson did his job on a bootleg throw to Zach Miller for a first down. A 1-yard rush and false-start penalty against Zach Miler set up second-and-14. The Seahawks did not block Jared Allen on the next play. Jackson had to throw away the ball. That set up a third-and-14 dump pass to Justin Forsett. Jackson couldn't have done much more with what he was given on that first drive.
The Seahawks asked less from Whitehurst when he went into the game. Whitehurst did a good job sensing pressure and throwing quickly to receivers open underneath the coverage. He appeared more comfortable and decisive than he frequently has in the past. He was completing short passes before the pressure could affect him too much. He averaged only 5.4 yards per attempt, but was efficient. He would have had a tougher time under the circumstances Jackson faced early in the game.
bry_paz expected the Seahawks' protection to struggle early while the team broke in a young offensive line. He thinks Jackson, unlike former starter Matt Hasselbeck, has the mobility to fare better behind shaky protection.
Mike Sando: Jackson did do a good job avoiding immediate pressure from Allen. He sidestepped the pressure and threw away the ball. A less mobile quarterback might have just ducked and taken the sack.
Northwest Guy thinks there should be no controversy at all. He thinks Jackson has already spent too much of his career looking over his shoulder. He thinks the team would be best served going with Jackson, who has a firmer grasp of the offense coming out of a short offseason.
Mike Sando: This makes sense. I did say Whitehurst has earned at least some reps with the first-team offense. I think that is true. But I also think coach Pete Carroll agrees with the premise that Jackson needs some consistent support after his career in Minnesota. Carroll could reaffirm his commitment to Jackson while saying he also thinks Whitehurst needs some first-team reps as well, out of fairness to him and in preparation for the season. Seems like Carroll could manage that situation.