Well, in Germany's case, if the free stuff did have a catastrophic impact on happiness, there would have to be something else really happy about Germany, offsetting it to make people more or less happy overall. In any case, you're right in being skeptical of my claim, conservative as it was, because causation is hard to establish. And the factors at play in Germany are different than that of the US, and the factors in 2019 are different than the factors at play in 1990.
But, I think about these things in terms of possibility. I think there's no reason why you can't make things like free education and healthcare work (i.e. why it can't be possible for them to work), if there's the political will to do so and you have competent people in power. But there is only some political will and mostly incompetent people in power. Diversity isn't a reason these programs can't work, it just gets in the way of allowing political coalitions to form that lead to smart policies being implemented and competent politicians elected.
When the people are divided on these issues, crappy politicians get into office that hamstring efforts to make these things work. The way you get them to work is: form a consensus in the population, get good people into office, and then hold their feet to the fire and make sure they act correctly.
This isn't easy, it gets at the heart of the dysfunction of the American political system. The first step is bringing people together, then maybe fixing the rot in Washington.