"Right to work" is American euphemism for your employer being able to fire you at will for no cause
Genuine question, because I don't understand the issue. If they want to join a union and pay the associated fees, they are welcome to. If they just wanna work a job without joining a union and paying their fees, they can do that as well. How is it a bad thing, unless you consider forcing those employees who don't care about unions to still contribute fees a good thing?
"Right to work" is literally the right to work for any employer who will have you regardless of whether you're in a union or not in a union.
You should question where you got the misleading definition of "right to work" and cui bono? by feeding you that misinformation.
The definition of US gun laws isn't "you can have most semi-auto rifles unless you've gone to jail, you live in California and the rifle looks scary, or the barrel is too short", but it's probably how someone would explain the practical outcome.