Most western cultures think that they've experienced moral progress over time. These aren't mere intuitions, however, as these observations often admit of some deep analysis. For example, some argue that our modern liberal intuitions (e.g. everyone is born free, etc.) are grounded in the philosophy of Thomas Hobbes. Hobbes was responding to earlier moral philosophy and was responded to himself in turn. Kant distilled these intuitions into a rigorous metaphysics of moral philosophy, which was still used quite actively well into the 70s.
Now, philosophers don't think that 'views have changed, therefore there is no truth.' Instead, they realize that good analysis of these earlier arguments reveals that they're close to right but skate around some important moral issues that can be unpacked with analysis. There's truth that can be found. It appears to all the relevant experts that moral thought is developing in a way that's strongly analogous to mathematical or natural scientific thought.
These are some of the reasons that subjectivism and relativism are extremely unpopular among experts.
Although we can observe and say that although there are people who have different moral systems than us, such as psychopaths and Spartans; we can actually scientifically evaluate the merits of the competing moral systems and their objective performance in the long run and historically. Historically, evolution has shown that altruistic humans are indeed "fitter" and objectively, game theory has shown that cooperative strategies are objectively better than selfish strategies in the long run.
You don't need examples or have to worry about cherry-picking. They're not ours to use. You can't humanely take a life of something that doesn't want to die.
Consider that neither the wish to be free from suffering nor the wish to continue existing is unique to our species; these interests are shared by all sentient animals, and indeed can be seen as fundamental biological drives. And if my interest in not being harmed or killed makes it wrong to harm or kill me when harming or killing me can be avoided, then an animal’s interest in not being harmed or killed makes it likewise wrong for us to harm or kill animals when doing so can be avoided.
Actually it's the most effective way.
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