If you feel that strongly against something then you voice your concern, loudly, and do not give ground. If the cost is your job then so be it. Better your job then your men. What price is your honor and the lives of those who serve under you. People die in war but if that is how these generals really felt, I'm suspect. They may be right or they may not be...their timing, however, is all wrong.
The time to dissent is not after you retire. My guess is they opposed these plans a lot more now then they did at the time the decisions were made. I'd also wager they oppose these plans in the media a lot more then they do in private.
Shinseki stood his ground and is greatly admired.