There's no such thing as univeral culture. You can't point at one society as being "perfectly right" and another as being wrong simply because their culture doesn't match your own. There have been many societies throughout history that have taken a far more robust view on what constitutes murder than our own.

I also dare say that in 100-1000-10000 years time, our descendants will look upon our culture as if we're no more advanced (socially) than the Romans, Spartans, etc

I used to play Table-top RPGs with people who played PCs who thought like this. Their characters were acting in a way that has been labeled "Murder Hobos". Not a very immersive approach unless one is intending to RP a psychopath.

There may not be a "universal culture" but there is a universal morality. Whether anyone likes it or not is rather beside the point. The moral life is full of grey areas but homicide, filicide and matricide are not found in the grey areas - again, not unless one is a psychopath.

@user23715 - How do you define a "universal morality"?

History is replete with examples of morality fitting culture rather than the other way around.

So kill your parents and let me know how that works out.

In Zurich, it's legal to kill your parents - en.wikipedia.org/wiki/Dignitas_(assisted_dying_organisation)

So how did it work out?

I haven't tried it yet, but the point is that there's no basically no moral absolute you can point at that some other culture hasn't considered not to be absolute.

Until 1992, In Uruguay it was perfectly legal for brothers to duel (to the death).

You should run it by your parents first and see what they think. As to your second item, I wonder why Uruguay changed the law? Must be that pesky universal morality impinging their cultural relativity.

There are a few countries where it's still legal.

And there are many things that are done in America/Uk that many feel violate their own conception of morality, such as abortion

Yeah, so is beheading for failure to convert. That makes some cultures relatively less moral than others not merely different. You keep conflating culture with morality. The two are not coequal - even, as your last example highlights, within one culture - let alone across cultures.

I'm still wanting to know how/what/why you consider to be a universal morality

And what makes your morality objectively better than theirs

If it was mine it wouldn't be universal now would it? I know it when I see it. Feigning inability or indifference in re to morality and its universal application is, as I said in my first post above, subsumed under the general heading of psychopathy.

I remain unconvinced.

But good chat. Some things to think about

Interestingly, without a universal morality (however poorly perceived) there is no grounds for debate. The fact that you not only engage in discussion of universal morality but initiate discussion is rather telling. Because, oddly, your mode of debate is consonant with never being convinced.