>>"You digress with attacking or killing. Which is worse? killing a child or leaving them to a life where they can't have relationships because some git used them."
I highly doubt those corresponding will be unable to "have relationships" because of sexting. One was 14, one was 17, and the third was a 32 year old FBI man. ;)
Now without details, there is a wide range of possible circumstances but there's nothing in the story to suggest that it was harassment or traumatic for the two girls (one of which would be over the age of consent anywhere in Europe, btw).
I don't know how long it's been since you were a fourteen year old girl but at that point attraction to older men is not uncommon. If she felt anything genuine towards this man, then learning he's been sentenced to twenty years for sexting with her is probably going to upset her more than a dick pic ever did.
Now none of this is suggesting that it is a good idea or right for a man in his thirties to be flirting with a girl of 14. It isn't for several reasons. But it is saying that you're wrong to assume that the girl is likely to be damaged psychologically or unable to be willing or even actively encouraging. Given what is said about the ongoing sexting, it presumably wasn't one sided as the two girls didn't just block him. As it never even made it to the point of following through (which we don't know if he would have or not and in one case it would be legal in Europe anyway), they were probably fine with it and it is unlikely to be traumatised.
This sentence has more to do with (a) American puritanism and (b) his being a Secret Service agent which invites a super harsh sentence as a means of deflecting damage to the organisation's reputation.