I'm a German who had a green card in the USA. I gave it up and moved back home to Germany. I value the European lifestyle over the American. I make less but I'm happier with being treated well.
I think the discussion is about society in general (healthcare, education, safety, work hours, leave from work, etc. ), not about how a person is treated in their individual workplace.
Europeans tend to be nationalist and if you're from the "wrong" nation you feel that. In America you won't be treated with more respect if you're from Denmark and not Poland. So that's an aspect.