I suppose one obvious response to this is "however much utility the billionaire can create by spending his wealth, a very much higher level of utility would be created by re-distributing his billions to lots of other people, who need it much more than he does". Money has a declining marginal utility, much like everything else.

Naturally, if you try to redistribute all wealth then no-one will have any incentive to create it in the first place, but this just creates a utilitarian trade-off on how much to tax, what to tax, and who to tax. It's still very likely that the billionaire will lose in this trade-off.