First, I didn't call him selfish for looking out for his own interests (As stated, if he is traded only a fool would look out for his former team. That team would trade him to a team without an offensive line if it offers enough return, as a result of which he could be ended for good in one game. Cassel would be well within his rights to refuse to restructure his contract, an action which could well serve as a dealbreaker in the trade and play out the year with the Pats.). Asante got tagged and threatened to hold-out until he got concessions in the way of an agreement not to tag him again. That hurts the team, hurts individual marketability (displaying an "I'll play when I feel like it" approach) and ultimately if called by the team puts that player under the same contract he failed to fulfill in holding out. As it is a violation of the CBA, it fuels animosity due to fines levied against the player. Most players abide by the CBA acknowledging it to be the rules of the game, few violate those rules.
Second, I grasp the concept of injuries and why a player wants money now rather than later. I know Cassel would rather have $30 million in his hand now rather than $14.6 million. My point was he has a decent chunk of change in hand to live off of (I am not rich but I suspect I could invest $14.6 million less taxes and retire on that without living in a refrigerator box and eating cat food) should anything happen to him injury-wise. I do not begrudge him that obvious motivation, nor do I call him selfish for wanting that money. The point is Cassel is not asked to accept the franchise tag - he is ordered to accept it under the CBA. He is a smart guy and knows he can either (1) hold out (that worked out well for Brady Quinn with his rookie contract) and try to force the team's hand or (2) accept the money and the risk of injury and play for the subsequent year's contract (which if he shows he is a team player, plays as many games as needed and further proves himself which may mean an even larger contract). And Cassel survived this year injury-free. Brady went 7 years without a major injury. If Cassel rolls the dice for one year, what are the odds he has a career altering injury, certainly in a season in which he likely plays only a few games (and yes, I know Brady was hurt in the first game but it was actually 7 seasons and 1 game given his consecutive game streak)? Does that probability justify proving you will fight the organization to further your own interests and after a season of success you have become a malcontent? I wouldn't call that a prudent decision.
Finally, NFL contracting blows as it is entirely one-sided. Players protect themselves with bonuses as everything else is illusory. I expect players to negotiate for what they are worth and to maximize guaranteed money. Veterans who have played for all the money they need can return for minimums or less than market value to attain career goals if they want to do so. Until they reach that point, get your money if you can. With that said, any shrewd negotiator knows a player's value is more than statistics and at least some of your value is in locker room presence/team temperament. My opinion is Cassel will acknowledge that consideration and take a decent paycheck knowing his doing so will likely put him further ahead (expecting the same bonus next year he would have received this year) than he otherwise would be had he taken the initial free agent deal.