Aiming for profit maximization at the expense of all other considerations is not fair or ethical. Trying to get the maximum possible profits while keeping in mind things like the safety of one’s workers is fair, ethical, and perhaps even required.
In order to be ethical, businesses have obligations to all of their stakeholders. This means that they have obligations to their workers and to their customers, but also to their owners. They cannot ignore the interests of any stakeholders while remaining ethical.
Therefore, it is not ethical to push for the absolute maximum in profits. That is, it is not ethical to put workers in dangerous situations simply because you do not want to have to pay to create safe conditions for them. It is not ethical to use child labor as a way of getting lower costs. Ideally, governments regulate such things, but if they do not, it is still not ethical for companies to engage in such practices.
Once the firm has ensured things like the basic safety of its workers, it has an ethical responsibility to make a maximum profit. This is because the firm has owners who have invested their own money in the firm and deserve to make as much profit as is ethically possible.