I understand that and even articulated that in my post. Additionally, the build cost and markup (profit margin) is much higher than commodity goods sold at Walmart. It has to be in order for yacht or luxury car builders to survive. Walmart couldn't sustain 40% profit margins and exist.
I don't care if the rich buy yachts, it is their money to spend. On a large scale, as outlined in the OP, and the entire point the article was making if it has to be clarified for you; on a large scale the income distribution being consolidated at the top is bad for the economy. If our economy is built entirely on rich people buying yachts, it is unhealthy and unsustainable. If we don't work to correct it now, it will correct itself eventually, and in a much more jolting manner. Also, if the natural course is correction, how can it be "bad" to correct it?