> Well, wars that killed tons of people were supposedly fought for "basic human rights" and "democracy" too, so there's that.

That's not a meaningful statement. It doesn't matter what something was supposedly fought for (Iraq was supposedly fought for WMDs). It matters what it was fought for (Iraq wasn't fought for WMDs).

> And whose to say? Some other country based on its own culture, and treating it as some some of universal laws of physics?

The people in Hong Kong or Japan are not so biologically different such that what causes their humanity to thrive, is entirely different from what causes the humanity of North Korea to thrive. Culture is a bogus excuse, there is nothing special about it that justifies oppressing people.

You answered your own question with the last part. We can easily prove out what is best for humanity, under what conditions humans best thrive. Yes, it in fact can be measured and easily demonstrated. We've already figured this out. It's no different than understanding that humans don't thrive when they're suffocating or starving or lacking water.

> That's neither here, nor there, because vaccines are the subject of scientific study, and results can be measured.

And that's where your entire premise falls apart. A human morality can be judged by its outcomes, very clearly. This is night & day in many cases, such as Cold War West & East Berlin, or current North & South Korea.

The actual outcomes of an applied morality can plainly be measured in numerous obvious ways. We do it all the time: we know for a scientific fact (yes, scientific fact) that the approach Denmark uses is vastly superior to the approach North Korea uses. We have measured the outcomes, we know what works. We have dozens of metrics of human life that we can measure it based on, such as life expectancy or access to basic healthcare. Morality is not entirely subjective: someone strangling an innocent person to death in murder isn't a matter of opinion as to whether it's good or not. That's a simple, obvious, baseline example proof that morality is not always subjective. Someone having an opinion on something doesn't mean it's right or wrong by itself. Whether a morality is good or not, requires one simple starting question: does this approach improve human existence; does it lead to demonstrably increased happiness and well being. The surveys of the happiest countries that persistently come out with eg Scandinavia on top, are not a fluke.

From basic foundations you can determine objective morality issues to build a society on, including whether eg murdering innocent people is proper to a society flourishing or not. We can measure how humanity survives, thrives, or fails under various conditions and create approaches that utilize rules of morality that are best to spur positive outcomes.

If this weren't true, the best outcome countries would all be scrambled, it'd be nearly entirely random. Sudan would be right up there with the Netherlands. You'd have repressive slave states routinely with hyper GDP per capita figures, low work hours, top notch welfare states, and leading all the happiness surveys world wide. Of course that's not the common outcome at all, it's exactly the opposite.