OK I'll put the negative case (and I've often put the positive over the years):
It's not impressive that a driver should choose to step out of F1, because he can't be assured of a championship winning car. Alonso went across to Renault, who looked crook when he went there. But he drove and showed that his ability and work ethic and charisma are as strong as ever. Its not impressive at all that he's stepping out of the game - unless the Ferrari payout excludes driving for another team, which I have not heard it does. Perhaps though it says that if he drives for another team, Ferrari will not pay him. But if his contract does not have such exclusions, then KR should be racing in F1 this year. Afterall there are many other teams available. There is now just one other drivers from his country in F1, and that driver has not been overly impressive (perhaps due somewhat to McLaren though).
There are also two Red Bull teams, not just one. If he was serious about RBR, then he'd show his stuff in the other team. One of their very youthful drivers could wait a year, surely.
But his manager says he's not interested unless he has a car capable of being a championship winner. That's what he's had all his career except for his first stint at Sauber. After years of great cars, he won't accept just one year out of a top car?
Get real - having such a car is not an entitlement. Its a gift, that has to be earned and justified.
The probability that RBR will be a championship contender for 2011 is not large either. They are a smaller team than for instance Ferrari and McLaren. They were fast in 2009 due to a rule change. But from a development competitive advantage, they are well behind McLaren and Ferrari. Its quite possible too that MB will increase the resources for their new team, who with Ross Brawn, maybe formidable in 2011.
Kimi's issues border on laziness IMO. He's also used to being paid a huge income - and at Ferrari, Massa who was on a fraction of KR's, eventually seemed quicker than KR, for quite a lot of the time too.
Very poor IMO and I'm not happy he's quit. But then maybe he shouldn't come back - his ego must be much more delicate than all the others in F1 it seems.