Abuse from peers and the community at large for sending nudes is heaped on girls vastly more than boys. I singled out girls for that reason although boys have certainly be subject to harassment. I absolutely think it's abuse for groups of boys targeting girls to "collect" their nudes for sharing and girls to take the pictures of other girls for use as bullying / shaming fodder.
Snapchat encouraged the idea that nobody but the receiver could ever see your photos, even though they knew this wasn't true. This takes perfectly normal sexual experimentation and turns it into a bullying service which they have done nothing about. Yes, it's the users' behavior but when a company aims at a young audience and then doesn't seem to care about their safety that it turns into something they're responsible for.
When I was in high school there was a similar shaming incident with a girl and a VHS tape. It's not the medium that's the problem. While I think the majority of the HN community would agree that snapchat has serious security issues, once the images leave the victim's handset it's a hopeless situation. In digital media if it's consumable it's reproducible (just need another camera). That's the lesson for the kids--not this app is or isn't "safe" for nudie pics.
I don't really see a good way to address the bullying issue. It's been more than a decade since I received my first lecture on the permanence of content published to the internet (by my 70ish year old school librarian no less). This isn't a new problem and it seems there's no shortage of regrets out on the WWW. It's safe to say the jury is still out on https://en.wikipedia.org/wiki/The_Right_to_be_Forgotten which is what I gather is at least the spirit of what you're advocating?
IMO who's responsible here are the kids and vicariously the parents. The parents need to educate their kids, pay attention to what the kids are doing, and support their bullied kids--even through the justice system if necessary. Less nudie pics created and more punishments of blackmailers are about the only things I think will help. Maybe snapchat not being so naive/deceptive with their security would help in the short term but my bet is any of the 100 other "secure" messaging apps would fill the sucker/idiot gap pretty quickly.
Snapchat encouraged the idea that nobody but the receiver could ever see your photos, even though they knew this wasn't true. This takes perfectly normal sexual experimentation and turns it into a bullying service which they have done nothing about. Yes, it's the users' behavior but when a company aims at a young audience and then doesn't seem to care about their safety that it turns into something they're responsible for.