This is not accurate. I've occasionally researched positions in Europe, and while I haven't looked at Denmark specifically, mid/senior-level software developer salaries tend to be around $45,000/year (or even less), which, before taxes, is about half of what's typical here in the Boston area, and a quarter of what's typical in the SF Bay Area.[0] Many European developers emigrate to America; next to no American developers emigrate to Europe.

I don't know what Danish fast food employees and store clerks earn, but I doubt they make more than software developers ($45,000/year is about $22/hour), so they definitely don't make "several times" what their American equivalents do.

Depending on the local job market and cost of living, a typical American entry-level salary for a new employee is about $10 (9 EUR)/hour, while a junior manager or semi-skilled worker would make $15-$25 (13.50-23.50 EUR), and a senior hourly manager or skilled worker would make at least $20 (18 EUR). Unionized and/or government employees make substantially more (especially factoring in benefits), although those positions are a lot harder to come by.

Keep in mind that the tax rates are far lower, possibly even negative depending on credits,[1][2] prices are also much lower, and, contrary to European popular belief, there actually are extensive federal and state social welfare programs for the low-income, including free healthcare.[3]

Now, I wouldn't say that people in those positions are making what I as an upper-middle-class professional consider a "good" living, but it's fairly comparable to other first-world countries. There's a reason the only Americans working in Europe are rich expats, not migrant workers sweeping floors and waiting tables.

Relatively speaking, the main socioeconomic problems in America are not so much that any of the people who have jobs are uniquely poorly-compensated, so much as chronic unemployment, downwards social mobility, the factors that contribute to those,[4] and that middle-class families must now take on a small fortune in real estate and college debt to raise children to the same middle-class standard of living.[5]

[0] The only place I've looked at that's even somewhat competitive salary-wise is Switzerland, the one country in Western Europe that's even more capitalist than America is. Also the only country I've ever visited where (driving 175 km or so) I never saw any visible poverty at all (or anywhere that didn't appear to be both prosperous and growing).

[1] https://en.wikipedia.org/wiki/Earned_income_tax_credit

[2] https://en.wikipedia.org/wiki/Child_tax_credit#United_States

[3] https://en.wikipedia.org/wiki/Medicaid

[4] Globalization/deindustrialization/automation, crime, broken families, drugs, etc.

[5] And it's still more difficult for those lower on the ladder, who can't take on that much debt.