I see your point and it's a valid one. If the sociopath sees the child as a competitor it may very well be damaging for the child. But I think sociopaths have the capacity to be protectors and providers at their core. If you look at people with these traits, they're fighters, they're firemen, soldiers, risk taking behavior may be inherant in who they are but I believe those traits can and have been used to benefit families and societies as a whole.
I know in combat I want the soldier next to me to be able to kill without hesitation (without emotion) I want him to carry on the next day without it tearing out his insides when we do our 10 click movement back to the COP. For these same reasons I think sociopaths make excellent providers and protectors of families. I believe their is honor among theives... just as I believe there is a type of love among sociopaths. It may be a fend for yourself kind of love, but I think it's there.