To use an anecdote, my mother in law has lived, for many years, on a peaceful dead-end street. Last year, an apartment building was put up at the end of the street more than quadrupling the number of families that lived there.
Since then, there are cars driving by on a regular (many times a day) blaring loud music. Her neighbor's big window in her living room has had rocks thrown through it on several occasions in the first months. My mother in law feels less safe going for walks, because she no longer knows most of her neighbors and this area of the city was already not exactly low crime.
Her perception of her new neighbors, and their behavior (both criminal and otherwise) have completely devalued her experience of living at her house.
Does that make her a NIMBY? Yup. Is her quality of life now lower? Yup.
Is it the fault of higher density? No.
It is the fault of a culture that tolerates disruptive behavior. Higher density has only brought more of it to her doorstep.