Allright, consider a situation where there is a very very small probability that something will work, but it gives infinite utility (or at least extrordinarily large.) The risk for doing it is also really high, but because it is finite, the bayesian utility function will evaluate it as acceptable because of the infinite reward involved. On paper, this works out. If you do it enough times, you succeed and after you subtract the total cost from all those other times, you still have infinity. But in practice most people consider this a very bad course of action. The risk can be very high, perhaps your life, so even the traditional rationalist would avoid doing this. Do you see where the problem is? It's the fact that you only get a finite number of tries in reality, but the bayesian utility function calculates it as though you did it an infinite number of times and gives you the net utility.