If a thing is an entity, and it is absolute, does it need a source?
If you are going to say that such a thing as absolute morality exists, then it needs to be grounded in something. You are either a deontologist or a theist. Given that you have said that you are not religious, one would guess that you are a deontologist?
I would say the litmus test for this is whether either of those acts limit or prohibit the creativity or free thought, or exercise thereof, of another person. If the litmus paper turns red, the act is evil.
What if I opened a can of worms and told you that free will is an illusion?
There are actually scientific grounds for saying this.
Toxoplasma is a parasite found in the feces of cats. If a mouse were to ingest this parasite, it would infect the brain and cause the mouse to behave differently. It would actually seek cats. The cat would kill and eat the mouse, and the life cycle of Toxoplasma would continue.
In a similar way,
Cordyceps (watch the video, highly recommended) is a fungus that invades the brain of insects. Insects then climb up the highest leaf they find, bite down on the leaf, and die. The fungus then germinates and sprouts out of the insect's body, where it can go on to infect other insects.
There are a number of brain infections (encephalitis) in humans that cause change in behaviour. For example, HIV and Herpes encephalitis causes psychosis and depression and is usually mistakenly referred to psychiatrists when what they really need is a lumbar puncture and some antivirals.
But there are more subtle cases as well, which do not involve infection. Suppose I were to introduce you to an individual who was rather disinhibited. He tends to say or act out the first thing that enters his mind with seemingly no thought for the social consequences. If he were to see an attractive woman, he would unzip his pants and show her his erect penis; or worse, rape her. He likes little boys and has a tendency to hang outside the school and try to entice them into his car with sweets, where he would drive them to a remote location and have his way with them.
You would think such a sociopathic individual is a menace to society, and as an evil individual he should be punished? Suppose I were to then tell you that he has had a brain injury that damaged his orbitofrontal cortex, and prior to this injury he was a responsible and loving father, who held a steady job as an accountant. Would you think differently of this individual now? Suppose he has
not had a brain injury, but his personality suddenly changed after a brief illness in which the doctors found nothing wrong. After he is executed for a rape-murder, his brain is preserved for science. 100 years later, new medical technology discovered that he had some kind of viral encephalitis which caused his behaviour to change. What would you think then?
There are even less dramatic examples. Human behaviour has been documented to change depending on the physiological state of your body. Do you think you can resist that fried chicken? Not if you are in a leptin deprivation state. Are you aggressive and have a tendency to beat people up? Perhaps your testosterone levels might be high. We are, in fact, prisoner to our hormones and multiple other influences that are yet to be documented. Or perhaps it might be fair to say, we are a product of our neurochemistry.
jazdoc I have met and spoken to Richard Dawkins a couple of times and he expressly does
not believe that we should base our morals on evolutionary biology. Rather, he agrees with Peter Singer and Sam Harris about a secular (i.e man-made) basis of morality. In fact, Sam Harris talks about scientific morality. A little too much to type on a forum post - if you are interested, read his book.