The "decisions" plants make can be explained by a cost-benefit analysis, where both the cost and benefit are closely related to survival. In other words, plants do whatever has the most net benefit to their survival. A similar cost-benefit analysis also explains much of human decision-making and behavior. Humans have a strong desire to survive, and we usually act accordingly.
Starting only with the reasonable assumptions that (1) plants are always morally neutral, (2) there is such a thing as moral good and bad, and (3) humans are not always morally neutral, it follows that moral choices are part of the anomaly -- i.e., what's left over after we subtract out morally-neutral plant-like choices & behavior. Thus, moral good is somehow related to the extent to which someone deviates from their optimal cost-benefit solution. In other words, moral good involves going against what's apparently in one's own best interests. But why would anyone do that?
The other major difference between humans and plants is that humans are aware of other people's needs and can consider or neglect to consider the cost-benefit analysis from the perspectives of others. Thus, moral good can be defined as the extent to which one chooses to sacrifice self-interests for the benefit of others. Moral bad, then, would include anything that isn't either morally good or morally neutral (i.e., an anomaly in the opposite direction). In fact, the majority of the world's problems can be attributed to one thing -- people acting according to their own cost-benefit analysis while ignoring or going against that of others.
According to this model of morality, a lot of what seems morally good may in fact be morally neutral at best. There are many social, emotional, and even financial benefits to being a good, generous, "selfless" person. We all want to be thought of by others, by ourselves, and by God (if we believe in him) as morally good, which requires doing morally "good" things and avoiding the "bad". When we act altruistically in order to maintain our "good person" status, feel good about ourselves, or score points with God, it's really a form of self-preservation and self-advancement that isn't much different from what a plant would do. And if we do it to get undeserved attention or praise, or to deceive people into thinking we're morally better than we really are, we've gone beyond what a plant would do; and that anomaly, I would argue, is on the wrong side of moral neutrality.
Some of the other interesting implications of this morality model include:
- Morality is both relative and absolute. The morality of specific actions depends very much on the context (i.e., is relative), but the fundamental principle of morality is absolute, objective, and universal.
- Intent matters a lot. The same action can be moral, immoral, or neutral, depending on the intent. And intentful thoughts can still be moral or immoral even if not acted on.
- "Good" actions are much more likely to be truly good if done in secret and/or with no apparent benefit to oneself. [Note: Moral good doesn't necessarily require complete lack of benefit to oneself. It just requires that a different choice would've had more apparent net benefit to oneself.]
- Morality is a full spectrum, not binary or black & white. There are different degrees of anomalies relative to plant "morality", so there are different degrees of moral good and bad.
- Following the "golden rule" (to treat others the way you would want to be treated) probably is, in most cases, morally neutral. The "platinum rule" (to treat others the way they would want to be treated) is better but still inadequate as a moral guide.
- Refraining from immoral behavior doesn't necessarily mean you're being morally good, particularly in situations where the personal cost of that immoral behavior (e.g., going to jail, friends thinking worse of you, etc.) outweighs the apparent benefit.
- Refraining from immoral behavior is more likely to be morally good if it's personally difficult to refrain from and/or easy to get away with.
- Doing what's morally good is never "worth it" from a personal cost-benefit perspective. If it truly seems "worth it", it might be morally neutral at best.
- Doing true moral good is very difficult and doesn't come naturally. If it seems easy or comes naturally, there's a good chance it's morally neutral at best.