Also, we need software to protect us from accidental disclosures, implemented as a browser extension, proxy or filter in the OS (like an antivirus). Privacy should be made simpler.
So don't post it online to begin with. There are things that simply shouldn't be posted online under any circumstances.
That doesn't only mean "don't sext", but also, for example, if you're a corporation or a public entity, don't have personal information stored in a server that's online unless it's completely necessary, etc.
By having something connected to the internet, someone can make a copy, and once the copy is made, there's no going back.
That doesn't only mean "don't sext"
SMS messages cannot be assessed as "not posted online" anymore, due to the nature of the software used by service providers in support of SMS services.
If you send an SMS text message, by default you are likely posting it to an online system, even if your device provides no obvious indication of that fact.
Reducing the ability to share information is just as much a violation of pricacy as some one "stealing" it and disclosing it them selves.
The problem with Facebook and the likes is that by default anything you post to them is no longer yours hence no longer private and no matter how much security options they give you the potential loss of privacy is the same.
One of the major issues with this debate is that people equate anonymity with privacy and as a positive thing, confuse privacy with secrecy and can't agree if all they want is effective privacy or principle privacy.
Note that in all of this, I'm not using Facebook at all and not even visiting it. But, I'm in their system with data about me that I didn't put there.