[injeolmi_love]

Because humans have a natural right to movement, helping slaves is not theft even if an evil social institution falsely claims it is theft. Similarly regarding eugenics, humans have a natural right to reproduce and to live, so someone assisting someone to escape that situation is in the right no matter what society they live in.

Extreme moral relativism like you’re mentioning here is just as wrong as utilitarianism.

It’s not preferable to steal than to lose the planet. Some things really are worse than death, and committing an evil action is wrong no matter what the justification the evildoer makes.

[dirtyv]

Evil is not a 100% settled matter. For example, some people believe that saving another person's life if you can is a moral obligation and to not do so would be an evil act. I gather from your refusal to even consider stealing something in order to save the planet you are in the other camp.

[injeolmi_love]

For most utilitarians, refusal to do good is evil because they view actions as having a certain number of positive or negative utils based on their outcomes.

For many other ethical systems, good and evil aren’t weighed against each other. Instead evil deeds may be forbidden flat out. Good deeds are optional but commendable. Since evil is forbidden and good is optional, you cannot justify good with evil - you cannot justify the unjustifiable.

Why is deontology a better system than utilitarianism? There’s a lot of reasons, but here’s two.

First deontology solves a lot of thought puzzles much more cleanly than utilitarianism does, and avoids the weirdness such as that torturing one person is ok if it makes everyone else happy (see the short fiction story “The Ones Who Walk Away from Omelas” for a empathetic example). Deontology has a strong philosophical basis outside of theology, especially beginning with Kant.

Second it prevents those in power from justifying evil deeds because of the good outcome. Take politics, where politicians will justify evil actions to their followers by arguing it’s necessary to prevent the other side from winning. If people accept a better theory of ethics, those types of arguments won’t take and politics will be forced to a higher standard.