and it does seem incredible that we put the technology into small mobile phones without ever thinking of the consequences
I'd look at it the other way - I don't think there is anything unethical in terms of consequences of people taking photos of themselves. What's incredible is that people support laws, without realising of the consequences in a world where cameras are so commonly available and used these days, including among teenagers. The problem is the laws, not the technology.
I suspect there is a digital divide. For older people, the whole idea of filming or photographic yourself sexually just seems bizarre. Digital cameras are relatively recent, and many people would have been sexually active during a time when video cameras weren't available (or affordable). When criticising the UK's "extreme" porn law, which criminalises images of consenting adults, one of the attitudes I came across from supporters of the law, when I raised the issue of people taking private photos of their own acts, was "Why would you want to do that?"
Yet now we don't just have digital cameras, we have mobile phones which make cameras ubiquitous - it's one thing to say let's get the camera, but a phone camera is just there. Of course teenagers are going to be using them sexually, and that's going to stay as they become older - who knows, perhaps in a few decades' time, we might at least get more sensible views of censorship and laws that criminalise possession?