These same folks went on to figure out the logistics of preparing food. So no, I don't think it's at all axiomatic that the people who disagree with nationalism are necessarily affluent in the slightest. In fact, I've found most solidarity with refugees and anti-nationalist movements in the working class. The overall community of folks I saw ranged across income brackets -- plenty of software engineers, tech folks, trades folks, unemployed folks...
I think that when people say, "They don't really mean it" or "their principles wouldn't stand up if it meant a disruption to their lives", they are not aware of just how much work folks are actively doing every day to live by those principles and invite people in.