A refusal to do business over a controversy has a First amendment claim to assembly and petition. No federal law has any business limiting such a claim outside of literal matters of life and death.

I can see an argument that the Commerce clause grants powers to regulate such claims, but unfortunately federal laws in pursuit of a Constitutional power are still subordinate to Constitutional rights (IMO). It would require a Constitutional amendment to so empower a federal law to override a Constitutional right (again, IMO, as I'm writing to your "legitimacy" question posed to the GP).

Neither. Both would be attempts at assigning goals to things that aren’t persons. Fallacy of teleological thinking.

Collectivism vs rugged individualism and exceptionalism with a serving of low empathy self interest institutionalized.

A good chunk is the late 40s geopolitical climate. Recalibrating for the cold war was already in progress.

1947 was one of the first red scares, with for instance then SAG president Ronald Reagan signing explicitly anti-communist statements.

Unions are always assault from capital; they just never really recovered in the US from the red scares.

They didn't vote for it, or against it. In most countries, citizens don't get to vote on individual laws. We vote people into power, who then hopefully don't enact laws that harm us. But as we all know by now, that's never stopped a politician.