The "working class" in that context doesn't mean the whole working class including those discriminated against. They tend to get ignored when talking about the good old days of the "in group" as usual. They had an artifically deflated labor pool that kept out competitors driving up their wages, effectively a cartel. This bigotry in labor was also the seed of their downfall as those excluded started their own and undid the monopoly on labor bargining. Cartels either hold the world back or are passed by it. The gatekeeping approach has failed recursively with non-union shop prevalence, increased automation paired with professionalization as opposed to trade shifts, and outsourcing.

From what little I can tell about many European labor union styles they avoided this shortsighted xenophobic fracturing of their bargining power.