The difference between the illegality of porn and of deepfaked porn is that the former is usually based on a purely moral argument (e.g. "porn is sinful" and allowing sinful behavior "corrupts people with sin", leading to more - and worse - sinful behavior) whereas the latter is based on a lack of consent.
Consent is the corner stone of most societies (it's what allows for contract law and thus the "social contract" to begin with). Note that deepfaked porn is illegal in every country in which regular porn is illegal, so clearly the concern isn't with the porn aspect of it. It's categorically more similar to revenge "porn" or CSAM in that the subjects of it don't (or can't) consent to its distribution (or even creation). Also note that in countries where deepfaked porn is illegal but regular porn is not, deepfaked porn produced with the consent of the actors and those lending their faces would usually be legal. Consent matters.
I personally agree that consent matters, but I see many ways to contrast that argument
It's ironic and revealing that nobody actually consents to a social contract then. Closest most come is voting, and perhaps that implicitly validates the laws. But that's not really consent.
So maybe this consent assumption is not so strong!
But philosophically the justification for a state's existence is the mythical social contract and most modern states require some level of consent for contracts within their legal systems to be legitimate (e.g. can't be made under the legal definition of duress, which usually at least means a contract is invalid if the other party is literally holding a gun to your head).
