There aren’t any.
Let’s take an example.
If you’re arguing with Joe Schmoe about the ethics of some new voting ID law, he might say, “Requiring an ID to vote prevents fraud.” You might counter with, “Requiring an ID makes it harder for many of the poor to vote, since they often face a maze of fees and legal barriers when trying to get an ID.” In other words, you pin your argument to fairness, and Mr. Schmoe pins his argument to fraud.
But you both agree that fairness is good, and fraud is bad. You have a common foundation.
Imagine you met someone, a certain Mr. Evil, who had the opposite moral framework. He likes stealing because it gets him money. He thinks murder is kind of neat, as long as he’s not the one getting killed.
What do you say to someone like that? How do you make a logical case for the “good” system of ethics?
You can’t, because there isn’t one. At the center of our moral fabric lies a gaping hole. That isn’t a judgment on us; it’s the nature of reality.
Believing in God, following His laws, doesn’t help this particular problem, because you still have to decide whether to obey God or not. If you simply say, “God is Love, but I’m not really into all that,” someone can respond with “That’s crazy!” but that’s about it. There isn’t a counterargument to make.
What about Buddhism – do they have an answer? I’ve never been a practicing Buddhist, so it’s hard to say for sure. But I’ve studied Zen pretty in-depth, and it doesn’t look promising. Buddhism is about avoiding suffering, attaining enlightenment, achieving universal compassion. All good things, but beside the point.
Some people claim that evil is logically inconsistent, because it doesn’t make sense to hold yourself to a different standard than the rest of the world (i.e. I’m ok with hurting others, I’m not ok with them hurting me). I call shenanigans. It makes perfect sense – when other people get hurt, I don’t feel it. Subjectivity matters.
(This argument also doesn’t have an answer for people who want total chaos, who embrace suffering in themselves as well as others, people who – like the Joker – “just want to see the world burn.”)
Philosophers call this the “Is-ought problem.” There’s no defensible connection between how the world is, and what we ought to do.
At this point, you may be wondering if I’m really serious. I can’t honestly think that right and wrong are just a matter of opinion – can I?
Well, yes and no.
Of course I feel very strongly about ethics. Of course I want to do the right thing. Of course I don’t want to hurt anyone. Of course I care.
But can I justify that? Can I argue for “Thou shalt not kill” any more convincingly than for “This sweater vest is nifty”?
No, I cannot.
Maybe this doesn’t matter to you. Maybe it all seems needlessly abstract. You might say, look, you know the right thing to do, so do it. What does the logic matter?
Well, I’m a computer programmer. I believe in the power of science. To me, the logic matters.
What about you?