For me (and some people at the time), the Triangle Shirtwaist fire is an example of the types of abuses that can happen in a capitalist system where workers are essentially viewed not as humans but as units of labor. Striking the right balance between regulation, which is necessary, and the need to create jobs is indeed an unsolved problem. The owners of the factory were almost completely unrepentant, and indeed their lawyers completely humiliated some of the survivors of the fire. One of the owners was even cited for locking doors and windows at another facility later on. We can't force business owners to pass an ethics exam before we place the lives of workers in their hands, so unfortunately I think the power of the state has to be used to protect the basic humanity of labor, and of course, part of this includes protecting the rights of workers to unionize.
For me, the main question has to do with whether there is any good way for the relationship between employers and employees to be regulated. It seems that having the government set up all kinds of regulations is not ideal. The government tends to get too involved in ways that can hurt businesses. Having unions bargain with employers is also not ideal because it leads to situations where there are too many work rules and not enough flexibility for employers. However, just letting the employers have their way doesn't work well either. We can see that in this terrible tragedy. So what is to be done? What is the least damaging way to conduct worker-employer relations?