Keep in mind that, in buying said yacht, he is keeping several hundred labourers, machinists, electricians, plumbers, mechanics, etc., employed.
For a while, yes. And a ship that size will require a fair sized crew on a long term basis. But for the same money he could have opened a children's hospital that would provide long term jobs for many more people (as well as the short term "construction" jobs,) and benefit society, rather than just benefit himself. If I drive my car into a crowd of 20 people, will you congratulate me for missing 12 of them, or condemn me for killing 8.
By taking far more resources (represented by money) than he needs he makes less available to everyone else, and is a drain on society. Not saying he should be killed, but if he were prevented from accumulating that much excess it would benefit far more people than it would harm. Killing him wouldn't solve anything, of course. The money would just go to his heirs and there's no reason to believe they'll be any more socially responsible than he is.
10 percent of the people in the world own 90 percent of the rescources, and this kind of disparity has always been an indicator of collapse. We're already starting to see it. GM and Chrysler are both bankrupt, and this is blamed in part on the Unions. The unions decreed that people in the auto industry deserved more pay/compensation than workers doing the exact same tasks in other industries. That's a disparity, and will hurt in the long run. The exorbitant salaries and bonus plans given to the execs is another drain on the company, and another disparity. In the heyday of US industrialism (the 1940 - 50's) Exectutive salaries were about 10 - 20 times higher than the average production workers. Now they are hundreds, even thousands of times higher. While the restructuring of those companies will eliminate the disparity between industries, it won't affect the disparities within the industry. The exec's will likely take a pay cut that's less percentage than the line workers, and the disparity of wages may increase. Especially since workers hired from now on will recieve a "lifetime compensation (includes wages, benefits, and retirement) about 40 percent less than workers used to. A newly hired exec can expect compensation about 25 percent less than before.
I guess what I'm saying is - while I don't think it's OK to shoot the guy, I think it's wrong to support this kind of excess. Actually, it's not impossible he does deserve to be shot, or at least imprisoned. For him to have come out of the collapse of the SU with this much money, there almost had to be some pretty shady manuevers pulled somewhere. You don't put a military grade missle defense sysem on your boat unless you know you've made a lot of enemies.