IMO, both employees and employers should be free to form what groups they please and negotiate what contracts they will. This includes contracts that forbid an employer from hiring non-union workers. But there should also be no law mandating such a provision. Of course subject to government regulation that supersedes contracts (health and safety, human rights provisions, others).
You should be able to negotiate with your own group of people to get certain benefits, and I should be able to negotiate on my own. And then we could see who really gets the better deal.
Personally I am confident that my own deal would be better, but I have no problem with other people deciding for themselves that they would prefer whatever deal that a union was able to negotiate.
Also keep in mind unionization is a freedom which is currently being infringed! I firmly believe that organizations should be able to draw up agreements with another! If a union and a company mutually agree that all the company's workers must join the union, I don't see a problem with that. The fact that our lawmakers are going in and writing backdoors so that this is serious government overreach.
Or the union can force you out of your job by forcing the employer to hire unionized employees only.
Here is why this is incorrect.
It is illegal to fire someone for joining a union. This is a right that all workers have.
For the same reason that it is illegal to fire someone for joining a union, it should be illegal to fire someone for NOT joining a union.
So take you pick. If you want full freedom of association, sure, lets do that. You can make whatever contracts you want, but you can also be fired for it, (ie legalize firing people for joining a union). I think I would be happy with this outcome, to be honest.
But as long as union people are receiving this protection, NON-union people should receive the SAME protection.
But then we do that exact thing when the product is labor and not plastic. Your freedom of association is on the macro level, as in you can go from firm to firm to firm and if that firm requires you to join the union you just keep moving, same as if that firm pays a low wage or has no health insurance or anything else.