If the person is a slut it wouldn't be libel but it would still damage reputation
Sure, in which case the person wouldn't legally be a victim. It's completely legal to tell the truth.
But that strays a bit from the point. Making fake porn of someone is a false reputation of that person's character, and thus illegal, but only if it actually causes damages to reputation (i.e. you distribute it). Or at least that's the line of argumentation I think someone would use in states where "revenge porn" isn't explicitly illegal.
Even if the person is a porn star, the damage is that the porn is coming from somewhere other than the approved channels, thus the damages. Or maybe it's lost sales. Regardless, there are actual, articulable damages.
The reason for the illegality is the lack of consent not the reputation damage.
Maybe in states where it's expressly illegal. I'm talking more from a theoretical standpoint where there isn't an explicit law against it.
If there's no explicit law, tht standard is defamation/libel or violation of a reasonable expectation of privacy.
we make exceptions for especially sensitive subjects such as sex.
That's the reasonable expectation of privacy standard (that applies inside houses when in bedrooms, bathrooms, etc, even if it's not your house). If you're doing it in public, there's no reasonable expectation of privacy, so I think a court would consider filming in that context to be legal.
Then again, this could certainly vary by jurisdiction.
I also believe that people who uploaded photos of themselves/their children did not consent to having their photos used to make sexual content
They don't need to consent for any use, if it's made available for personal use, then any individual can use it for personal use, even if that's sexual content. As long as they don't distribute it, they're fine to use it as they please.
If you want control over how how content is used, don't make it available for personal use.
but from what you said you think it would be okay
Yes. I certainly don't want them to do that, but I really don't want to live in a society with the surveillance necessary to prosecute such a law. Someone being creepy with pictures of my kids is disgusting, but it honestly doesn't hurt me or my kids in any way, provided they don't share those images with anyone.
So yes, I think it's a necessary evil to have the kinds of privacy protections I think are valuable to have in a free society. Freedom means letting people do creepy things that don't hurt anyone else.