I agree that the lure or paradise and fear are both probably the main motivators for people considering the religion more important than family. But I also remember scriptures being read in Matthew (can't remember the exact verses now) where Jesus one must hate his father and mother to follow him and other scriptures that said one must love Jesus more than one's family. The JW party line dogma was that love for Jesus and God was the biggest motivating factor and that the paradise was a nice gift, but secondary to our love for God and Jesus. And I actually told myself in my mind that I was doing this primarily because I loved God although I wanted to be in paradise. But to be honest with myself, if there had never been in promise of reward, gift, "underserved kindness" (I've only been out a year, some phrases are still with me), I probably would not have hung around as long as I did.
On another note, I really think unconditional love is very rare. If I decide that I want to kill my mother, I think my parents would have good reason to stop loving me. However, I'm sure there are some people out there who truly do have unconditional love. I think most people would agree that religious beliefs would not be a condition for love even if it is dependent upon some other conditions..
Disclaimer: I don't have any children, so I don't claim to know how parents really feel.