the members of blue collar unions are still primarily conservative

This is false https://pro.morningconsult.com/analysis/labor-union-members-more-democratic-less-liberal

This is just simply false. Every major study has shown that an increase in union membership decreases bigotry of all forms. They also show that Democrats win more votes in areas which increase the amount of people in unions, and lose elections when unionization drops (rust belt is a great example).

The causal link is also not difficult to understand, a union forces you to work together with your fellow workers of all backgrounds and makes it clear that your struggle is deeply connected to theirs. It allows people to see that all workers have a lot more in common beyond just the level of race, gender, sexuality, or religion.

Nobody is claiming it is an easy cure, but it is a very effective treatment.

https://www.statista.com/statistics/1184429/presidential-election-exit-polls-share-votes-union-membership-us/