It was never an excuse, it was an explanation. The term "the abuse excuse" was coined by Alan Dershowitz. Given his reputation, his connection to Jeffrey Epstein and his tendency to defend abusers, 'nuff said.
If you've seen the first trial, there is more than enough evidence that the abuse took place. The photos of Lyle and Erik,'s genitals, (found in an envelope with the mother's signature on it) is hard to overlook. Even if you buy into the, in my opinion, ridiculous prosecution theory that eight-year-old Lyle and six-year-old Erik took the pictures, there is no reasoning whatsoever for the parents to save and keep the photos.
In the first trial, the prosecution keep changing motives. First it was the greed theory, and when the evidence proved otherwise, then they switched to motive to hatred, and despite the abuse, the brothers expressed love for their parents and wanted to be loved by their parents. Then it was the control theory, which originated from the discredited Dr. L. Jerome Oziel; the December 11, 1989 tape, is his theories, and the brothers simply parroted his theories, because they had already decided that they weren't going to tell Oziel the real reason why they killed their parents. Erik even said at one point in the tape, "What I did, I did because I had no choice." Lyle and Erik loved their parents and wanted to be part of their lives, as long as the abuse stopped.
MOO.