The point he is making is valid: these groups are not randomly selected and are not representative of one another. Hence, it is not that simple to extrapolate from one to the other.

Would free healthcare reduce deaths in uranium miners that are smokers? Probably some, but would it bring that to the same levels as non-smoking, non miners? Unlikely so. Hence it would be silly to pretend all the cancer deaths are due to lack of health care.

The smoking uranium miner example has a surprisingly realistic story, comes from real data; the dangers of radon in the basement were deduced from comparing cancer rates in smoking uranium miners with high radon in their basements, then they removed what they thought was the smoking and uranium contribution, then fitted to the general population.

It's valid within the argument structure but not to universal healthcare

My kid made a valid point that there was indeed a green MnM on the sidewalk next to the park.

Still didn't let them eat it.

It's a valid point in its own little bubble but other valid points mean more.

Stats are everywhere but stats that matter are rare.