"Greater Good" is a type of excuse where a person attempts to justify behaviour that a person with good desires would not have performed by appealing to some other, greater and more important interest that a person with good desires would have had.
Here are two examples in which the excuse of "greater good" is applicable.
Example 1: A driver is in her way to a meeting. On the way, the car ahead of her blows a tire and runs off the road. The driver stops to aid the people in the other car. She tries to call for help and discovers that there is no cell phone coverage. While she stays to help the victims of the accident, she sends the next car ahead to call for help. As a result, she leaves the people she had promised to meet waiting for her - a state that a person with good desires would want to avoid.
Example 2: A father and daughter are out fishing when the child is stung by a bee. She starts to get an allergic reaction. The father cannot find the keys to his own car. However, there is another car nearby with the keys inside. The owner of that car is nowhere in sight. He throws his daughter into the car and speeds her to the hospital. A person with good desires is averse to taking the property of another without their consent. But he is also averse to letting his child die.
In both of these cases, the agent appeals to a greater good to excuse their action. The greater good is a desire that, in a good person, would have outweighed the violated another interest that, admittedly, the good person also would have had.
In offering this excuse, it must actually be the case that a greater good has been served. In desirism, this means that, in this case of conflict, the agent acted on desires that people generally have reason reasons to promote as the stronger desires. Speeding through a school zone to make it to work on time because people have reason to promote a concern for the welfare of children that is stronger than the aversion to being late.
One of the things we see in this excuse of Greater Good is that people generally have many and strong reasons to promote a number of different desires - not just one. They have many and strong reasons to promote an aversion to making promises, aversions to taking the property of others without their consent, a concern for the well-being on one's children and for strangers in need of emergency help, among others.
Furthermore, people have reason to make some of these desires stronger than others.
Sometimes, these different desires come into conflict. When they do, an agent can appeal to the excuse of Greater Good to claim that she acted on the desire that people generally have reason to make the stronger desire.
However, we still expect to see evidence that the weaker desire was in play. The agent must show some frustration over the inability to have objectively satisfied the weaker desire.
The woman who missed the meeting is expected to contact those left waiting and apologize - reporting that she appreciates the fact that a good person does not break promises, but she broke a promise. She should offer to make it up to them. The father who took the car is expected to apologize to the owner and seek to minimize and to compensate for any harm done.
In both of these cases, the agent is communicating to the world, "Yes, I was properly averse to breaking the promise or to taking the car. I hate the fact that was forced to do so. I would have avoided that situation if I could."
As a part of our Greater Good ritual, the victims are then expected to forgive the agent. In doing so, the victim acknowledges, "You acted on the better desire. I recognize that an agent with good desires would have done the same thing and that there are no good reasons to condemn your behavior, so long as the legitimacy of the weaker desire is not simply dismissed."
One reason that the lesser desire must be in play is because it motivates agents to avoid the conflict. An agent with an aversion to P and an aversion to Q has reasons to anticipate and avoid circumstances where they must choose between P or Q. There are people who seem always to be missing appointments or failing to promptly pay back small loans. They seem always to have an excuse. However, with enough evidence, we can start to suspect that the agent just does not care about the lesser duty. This conclusion makes the agent worthy of condemnation. People have reason to promote an aversion that would minimize these types of conflicts.
Another sign of the lesser duty being in play is that the agent tries to resolve the conflict before sacrificing the lesser duty. The woman missing the meeting is expected to call and say, "I can't make it," if she could. The father looks around for the owner of the car and is desperate to seek permission before concluding that there is no time to waste. Both express frustration over not being able to do both. A lack of concern over the lesser duty means that its harms are not prevented.
Desirism explains these aspects of Greater Good because morality is not concerned with rules or natural laws weighed against each other. It is concerned with the weighing of desires that people generally have many and strong reasons to promote. It is the property of conflicting desires that they motivate agents to avoid conflict and frustrate those who must choose. These are understandable elements of the practice if excusing a wrong by appeal to a greater good.