But if you don't have some moral or ethical objection to exploitation, why do you have a problem with capitalism?
Because exploitation is contrary to fundamental human nature. And it won't do to say that it can't be contrary because human beings do it (exploit one another). Certain things people do are consonant with what is fundamental about human beings, and certain things aren't. Our notions about human nature are also the basis for ethics (assuming we don't believe that morality is ordained by God). This is why all apologies for capitalism, as well as slavery and other forms of class society, are invariably based on some argument to the effect that the class hierarchy reflects natural differences in human capacities, and arguments against class society on arguments that it doesn't.
Jim