Should a person found guilty of sexual abuse who had also being abused as a child receive a lighter sentence than someone who had not been abused?
No. They should get the same sentence, plus psychological counseling.
I wouldn't think that would matter to the victim(s) at all. Nor should it matter to the jury. Do the crime, do the time.
Nope.
No, all child abuses know that what they do is wrong.
No.
While homicide may be justified in certain instances; I simply cannot imagine that there is ever justification for abusing a child.