I've heard them defend themselves with lovely tales of family bonding, by saying that trophies serve as a way of reliving and appreciating nature, and by claiming they are responsibly conserving wildlife. You want to appreciate nature, take a walk or go camping. You want to bond with your kid, do it non-lethally. You want to relive the moment, use your flipping memory or take a picture. As for conservation, this has some merit but only when a cull is necessary to control overpopulation. Then, feel free to take your morbid memento and smear blood on your kid.
Killing for a bonding exercise, pleasure, or ego, is evil.
Appreciate nature by leaving it the Hell alone, it can take care of itself. It did so long before we came along. We've done enough damage.