The main reason that improvements should be made to the working conditions for low wage workers is so that the country could have an economic system in which there are better opportunities for people without a great deal of education.
In America today, we are moving towards a system in which the well-educated do pretty well but those without education are stuck in low-end jobs. These jobs do not pay as well as they once did, which means that people who are less educated are falling behind the rest of the country economically and socially. This is a dangerous situation for our country because it runs the risk of creating a country that is deeply divided. A democracy works best when all people are relatively equal to one another socially and economically. If we move towards a situation where there is too big of a gap between the haves and the have nots, we run the risk of creating class-based animosity in the country.
There are any number of reasons why there should be improved working conditions for low wage employees. One reason that comes to my mind is that better working conditions create more productive employees, a benefit to employers. Another is that better working conditions lead to less employee turnover, which is good for employers and employees. A third reason is that better working conditions tend to prevent unionization, which employers tend to think is a good thing. I should also add that in many instances, improved working conditions are a matter of state and/or federal law, for example, laws that require a safe working environment for most employees. Additionally, in a country that says it values human rights and decency, should not all employees have good working conditions, no matter what their wage level?
As you work on your essay, no matter what reasons you give to support your thesis, I want to offer you some advice. First, it will help you to keep your focus if you are able to define what you mean by "improved working conditions." This term could cover so many different areas, and I am not sure you will want to leave it to your reader to decide what you mean when you use this term. Second, as you develop your ideas to support your thesis, work on using examples. If you want to show that productivity increases, explain what kinds of improvements might allow this to happen. You might do research on this, or you might create hypothetical examples that rely on common sense or on your knowledge of various work environments. If you define your idea and use good examples, you will keep on course much better and persuade your reader more effectively.