A wage that is agreed upon by both parties without coercion is not, by definition, a 'slave wage'. Yes, there are poor people who live in hellholes and are used to much lower salaries than you and me. It may make us feel uncomfortable or guilty, because we don't 'feel' as if we 'truly' deserve so much more money than them. But thankfully, following irrational feeling of injustice is not the only foundation of ethics that we have.