It isn't my Nieces and Nephews that have been put off as you have phrased it. In fact I do occasionally see them the problem that my siblings are ignorant about mental health illnesses believing that anyone suffering from them should be locked away from 'normal' people and worse than their ignorance is their unwillingness to listen or learn about the subject. My siblings have therefore with drawn any and all contact with myself, however if I'm visiting my parents on my own I see the kids when they're dumped on my parents.

Most people who have children do it to fulfil their own needs/wants . . .
If it was purely an act of selflessness more people would adopt as a first resort ! But years of evolution and preservation of the human species means we are drawn to pass on our genetic material !