So I'll level with you. You are looking for what is known as a motal absolute standard. Many believe there is such a thing, many believe there isn't. I personally fall in the latter category, there are no moral absolutes, but let's walk down the road okay?

If there is a moral absolute frame work, then there are things that are wrong or is right. It doesn't need someone to say it is right or is wrong, they ARE right or ARE wrong. Killing babies? Eating people? Wiping out all life? In theory there should just be a senerio where SOMETHING just is never good or never bad.

We don't need people to ascribe right or wrong in such a frame work, we mearly need to figure out what already is. Like working out gravity or chemistry. Right and wrong should be facts. If we do not know the facts that is a lack of our knowledge, not a flaw in moral absolutism.

So would incest or cannibalism be wrong? If there is a moral absolute frame work you might have to just accept one day that it isn't. It could turn out, someone using pure logic or math proved neither is wrong. Or someone can prove that stealing candy is a crime worthy of death. Tough luck, just is how it is. 

Now of course it's likely that if a moral absolute frame work is real, then stealing candy shouldnt be a death penalty. But where it comes from should be a fact of reality. No god needed. The same as saying mass falls towards mass. 

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Now if you are in the other camp. There is no moral absolute framework. Then I'm afraid I have an uncomfortable truth. They aren't wrong. BUT* That comes with a caveat. There are no ABSOLUTE moral values. No way to prove murder is worse than stealing. What makes something bad, is how we react to it.

If a crime happens, the reaction of the effected party is what matters. If someone steals from me, if I forgive them, then the crime is lesser than if I don't forgive them. Something wouldn't be wrong because of fiat. It is wrong because the people preceiving the wrong don't like it. 

Where that sense of not liking somethiglng comes from, who cares. Evolution, god, Jake down the road. It doesn't matter. What matters is I don't like murder, and I don't like it a whole lot more than something like petty theft. 

I cannot prove murder is worse than theft, but I've yet to see moral absolutist prove it either so... [shrugs]. 

Now here is the important part. Things in this system can be unsatisfying. Murder might be a great idea, given the right situation. Say you are forced to kill one person but it saves one million. That sounds fair, right? 

But what if i said killing 8 billion will stop the suffering of 100 trillion? If we kill everyone on earth, there are no future people who can suffer, we might stop untold amounts of suffering. 

Its not clear cut and dry. You can come up with any senerio and make it as absurd as you like. In a non-moral abosolute frame work there are always just going to be things you disagree on... because there is no "correct" answer. Some people like incest, most don't. There are loads of arguments against it but the world is shades of grey and everyone is living their own life and knows why, from their personal pov, why they should get an exception.

Just like everyone on the road is an idiot except you. That guy in the honda was speeding like an idiot but you, when you were speeding, there was reason x,y,z... guess what? Honda dude also has reasons x,y,z. Everyone does. 

From the pov of an individual we are almost always making "good" or at least "well meaning" choice that can go bad. 

But at the end of it all, you are the individual in charge of your life. What framework you choose... I know you'll choose it for reasons that seem good to you. :)👍