Except when all the jobs in your industry are union jobs.

Unless you're suggesting someone in this position should have to retrain for a different industry. Which, sure, ok, I guess, but the cost to do so might be quite high to the point of being life-ruining.

Those workers are also free to use right to work laws, to make it so they are allowed to get jobs at whatever company wants to hire them while also not joining the union.

And then workers who prefer the union, can join members only unions that are not forced to represent people not in them.