I’m posting this as an answer in addition to Slytherincess’s because it would be too long as a comment.
I'm bothered by JKR's statements on this, because they imply that a child of rape is somehow defective because of it.
They do no such thing; that’s putting words in JK’s mouth.
What they do imply is exactly what they say: Merope failed Tom Riddle Jr by her complete misunderstanding of love.
- Her first failure was to bring a child into a loveless union, which has been conclusively proven time and again (in many forums beyond this one) to be detrimental to a child’s emotional well-being. Not because of the loveless conception, but because of the child’s relationship to his/her parents!
- Her second failure was to abandon that child herself. This should be more obvious: children whose parents leave them are not a mystery.
Merope was herself mistreated in the extreme. You could easily argue she had never experienced true parental love (Dumbledore does just this in his discussions with Harry). Her concept of love was not healthy — It was that of infatuation and power and escapism.
So after eighteen years of abuse at home, she finally escapes with power to make a handsome muggle want her. Why would she behave differently? This is how she was raised: power and control. She didn’t love Riddle, she saw him as an escapist ideal which she, through her witchcraft, could make happen.
And not knowing the difference, only knowing that she felt happy because the guy was paying her attention and acting like he cared about her, she made the mistake of forgetting the disparity between reality (Riddle was a jerk who thought her repulsive) and fantasy (Riddle cared about her).
And when that failed, she did not have the emotional resources to recover, to love her child (who was proof that the father “loved” her, and not yet having learned to love) she gives up and dies, leaving the boy. The psychology of this is important, and is real outside of HP.
Thereafter, JK spends large portions of THBP having Harry and Dumbledore explore the consequences this had on the boy Tom Riddle, a boy who thought he ought to be special but was instead abandoned by people who should have cared about him, to have loved him, but who were both incapable of any actual love.
Remember, Riddle first thinks his mother non-magical, because if she were, she wouldn’t have abandoned him and died. Then he learns the truth of his father’s indifference, and the glass is fully shattered.
Now, many, many people grow up in unloving homes, just as Merope and Riddle Jr, but few grow up to be like Voldemort. That said, those that do come almost exclusively from that same cohort: broken homes where love is not known; only power and control and indifference.
It is no stretch, then, that Voldemort does not love. To him, it is a lie that only leads to pain, and is only useful for control. Again, this happens in real life, and has been heavily studied among the better-known assassins in recent history.
Being raped is not suggestive of a horrible, dark, unloving future. Many children conceived by rape grow up in loving homes. But it is one possible first step in many where a child’s emotional psyche may be destroyed, and a good symbol of the overarching problem that leads to that child’s trauma.
Remember, avoid dealing in absolutes when looking at consequences.