1. I don't think the judge has to believe the justice system is flawed. It might just be that the justice system has limits, and that sometimes those limits are not sufficient to bring about the best outcome. Again, consider prosecutorial discretion and how it is used.
2. I don't think the judge has to believe it is flawless. In fact, the judge might believe that it is not flawless, and again exercise in the opposite direction of NOT sentencing someone who would otherwise be correctly sentenced just to keep kids out of a bad foster care system. My point was that, barring a situation where the judge has grounded suspicions about the foster care system, the judge must basically (as a principle of law) endorse the foster care system as a viable caretaker of the children. Judges would otherwise be required to initiate investigations into foster care systems (and the like) whenever they might be utilized in a legal setting. That's an impossible burden.
1. The judge must understand that the (justice) system is flawed, it's his/her job to bring about justice anyway.
2. The judge must believe the (foster care) system is flawless, it's not his/her job to worry about that.