Let's face it, we fall to temptation easy enough when there is no greater good to be accomplished by it. Most of the time when we sin it's for entirely selfish reasons with no real consideration for the big picture. How much harder is it not to sin when that sin seems justified?
One of the first illustrations I thought of was Robin Hood. Stealing from the rich to give to the poor. For Robin Hood, the end (providing for the poor and hungry) justified the means (stealing from the corrupt and oppressive rich). You could say that the rich deserved it, and I would agree that they did, but that doesn't change the fact that stealing ins sinful regardless of who you are stealing from. God shows great concern for the widows, orphans, downtrodden and the poor, so the temptation to steal resources in order to help them would seem justified.
Had Jesus bowed to Satan and become the king of this world at that moment, the entire world may have avoided 2000 years of suffering, war, famine and pain. If any sin ever seemed justified, that would be it. But the end didn't justify the means. Instead, we all would have been worse off in the big picture because salvation would not be available through the almost perfect blood of Jesus.
Mike @ DCC