"Cruel" is not an applicable word here; it could only be used to describe the way you kill an animal, like with a slow-working poison, but not the reason why.
There is nothing wrong with hunting a trophy if you use the trophy's meat just like you would any other legal specimen's. Trophy hunting can become a problem when the quest for a super trophy at all costs supersedes good hunting ethics.
There are places where, for a few ten thousand dollars, you can kill a super B&C trophy elk inside a fence; for every few points, the rate goes up a few thousand. This is hotly debated on some hunting sites, but for me there's nothing there to debate: That's not ethical hunting, that's an execution (unless you're a disabled veteran in a wheelchair or have some other really good excuse).