I think anti-union sentiment comes from the practical reality which is if you go to union-towns, they often look bombed out and horrible. The UAW, arguably the largest private union in the US, was founded in Flint, Michigan. The union didn't care about the city or its future, it simply sucked money out of the economy until there was nothing left, and then they ran off to DC. Conversely, industry towns without unions are usually nice places to live as the companies continue to invest money in them to attract more employees. This is a pattern we see over and over again, and in my opinion has led to the strong anti-union sentiment we see all over the midwest rust belt.
Grew up in the rust belt of Michigan, but not with parents holding unionized jobs, and still live elsewhere in it (also without a unionized job). Can't say I've seen the same sentiments or patterns be as common as presented. Of course I've always leaned towards supporting unions so that colors the perspective a bit too, but, in general, approval of unions in the US has actually been in an upswell https://news.gallup.com/poll/694472/labor-union-approval-rel...
There are obviously areas with decline for sure, e.g. the auto industry, but unions are usually seen as lessening the impact of that on the workers rather than the source of blame (not that everyone holds a single view). E.g., for the most part, people don't blame the union (or non-unionized industry) for the problems in Flint as neither is meant to privately fund e.g. the water pipes. They blame the downturn of the auto industry, which then gets into whatever reasons one prefers to assign. For some that's unions, but it's not actually been a very big mind changer on that aspect.
