I think you're missing something about Utility - specifically that ethically, if we're going to talk about this notion of utility, we should increase aggregate

I think you're missing something about Utility - specifically that ethically, if we're going to talk about this notion of utility, we should increase aggregate utility (the sum of utility of all people). The utility of money to a single individual decreases as the individual acquires more money, i.e. utility of money is higher for poor people and lower for rich people. This notion applies directly to the things purchased by that money. The aggregate utility (benefit to humanity) of a yacht that a single individual purchases is therefore far lower than the aggregate utility of a bunch of smaller things that are purchased by a bunch of less wealthy individuals. And then what follows from that is by purchasing yachts, you are promoting an industry that lowers aggregate utility. It can be argued that if you're going to "feel bad" about money, this spending is what is the potentially unethical part, which was the author's point.