Well idk about this case in particular, just read a bit about this, but to me as soon as there is boundary crossing, it's already a bad thing, specially on children or young teen, and there can be many things surrounding the abuse, related to secret, psychological pressure, that can still have negative impact on familly climate, of feeling of safety at home, and that can easily snowball into bigger and bigger thing, into problem at school, into other problems, and even if maybe the act itself is not taht bad you could say normal reaction of a teen that has hormonal growth, there can be many things surrounding it that can still have negative impact on the person, and specially when there is some level of secrecy or pressure or other bullying that can escalate it can still be a good start for other bigger problems, it depend also if the person is well surrounded or not, in a good supportive neighborhood or not etc
well an ex of a friend this kind of things is going on a bit in her familly, i'm not sure about the whole thing or anything, but it's this kind of things of already big brother a bit bullying her, but her familly looks a bit crazy too, it's with her a familly that a friend got an ex military with the ak47 tatoo, they seem to be pretty violent also, even if i don't think they have really hit her, but having bad famillial climate like this, it can still end pretty bad, with teenage problem who can end with the police or psychiatric hospital and lead to more trauma and more problems.
As for victims reproducing this kind of action on other, it's hard to say, there was a good documentary in french on this issue, specially related to incest or familly abuse, and the affective relation the person develop with the abuser can also be mixed and lead to many problem in how to conceive love and familly relationship too, in this documentary they were saying from psychiatric/clinic experience that a large part of abuser of this kind have been victim of it themselves too, but it's not always the case either.
There is an association in france who deal with this, with people who might think they can have some tendencies they have hard time to handle often mixed with other psychological issues or trauma they have hard time to handle themselves, but there can be many bad consequences when this kind of things happen and people don't get help.
But well this issue in particular it seem a lot mediatic thing to shock a little bit the american public and put a bit of spice in things to make more audience or to launch discussion on this topic, but it's clear they are always very taboo things, it's generally very hard to speak about this kind of things with most people. Which in itself to me is also part of the problem with this kind of abuses.
http://www.alternet.org/belief/did-jim-bob-duggar-admit-fundamentalist-families-have-sibling-molestation-problem :p