I have to problems with Right to Work laws.
People should be free to join the union and leave when they want to. They should also be free to negotiate their own employment terms.
You might be thinking of salaried, white collar employes, some of whom can already negotiate their salaries and/or raises. The rank and file workers (such as factory employes paid hourly) aren't as likely to have much success with their attempts. Hourly employes typically fare better when they act as a group (not necessarily a union).
The problem with individuals negotiating on their own is that there are others who are doing the same or comparable work for the same company, however, are paid differently. People have ways of finding out about these things, and often the result is animosity. We do see this with salaried employes with the difference starting from day one.
The parable about the laborers in the vineyard comes to mind. That's the story about the workers who toiled all day, ending up with the same pay as those who came late and worked for only an hour.
When economic conditions are highly favorable, many employers do what they can for their people, having the means to easily do so. When times get rough, the pendulum shifts, and often disgruntled employes are simply told: "Just be glad you have a job."