I don't know, I think that's debatable. There are genetic predispositions to psychopathy and it is implied that since Freddy's father was in the hospital for the criminally insane that Freddy inherited that predisposition. So while it may not have happened exactly as it did in the movie, not being put up for adoption does not necessarily preclude Freddy from eventually becoming a murderer.
In fact, if Amanda had left her order and raised Freddy, things may have been worse. While Amanda's rape was not Freddy's fault, it is often very difficult for a raped woman to create a positive emotional attachment to a baby produced from that rape. While this is extremely unfair to the baby, who has done nothing wrong, it is nevertheless very often true. As far as Amanda was concerned, she was raped by 100 men hundreds of times, and having her raise Freddy might have actually been worse for Freddy than it would have been if he hadn't been put up for adoption. It would have been difficult for Amanda to form a truly loving bond with Freddy and she may have made him worse because of that.
And again, to make this very clear, I am not saying that is Freddy's fault because it's not. You cannot blame a rape baby for the actions which caused his/her birth. It is also not the fault of the baby how the mother treats them. But fault doesn't change reality. However, very, very often it is much healthier for these babies to be adopted because adopted parents don't connect the baby with the rape. In Freddy's case, however, the fault seems to lie more with the agency that adopted him out than anyone else. If they had put him with a decent and loving family rather than a single and abusive alcoholic (which is VERY unrealistic), perhaps he could have received the loving and nuturing environment every child deserved, that he would not have gotten from Amanda. However, if that happened, these movies would really suck.
