It scares me that we can tinker with so many things genetically. And, more to the point, that we do it simply for the sake of doing it.
Stupid.
They're not doing it "for the sake of doing it." They're doing it, partially, because these same techniques could be used to treat a lot of diseases. They can experiment on either mice or sick kids, and quite frankly sick kids cost a lot of money.
Even if they don't have any particular reason for doing the research, so what? It's potentially useful knowledge.
Why would we ever want to get rid of fear?
They got rid of a smell receptor, which apparently destroys a mouse's ability to recognize a cat as a cat. They were probably inspired by the toxoplasmosis parasite, which does something very similar.
This would all be incredibly obvious to you if only you had been reading psychobiology research, oh, around the time I took that psychobiology class.