The lawn mower is not a business. It is a piece of machinery. The business that designed the lawn mower can ensure the design is safe, at least within reason, through the proper engineering of the product and by instructing its users on the proper use and maintenance of the machine. There is nothing inherently unethical about manufacturing lawnmowers unless you consider the practice of mowing lawns unethical (which there are legitimate arguments for, but I don't think that was your point).