Okay, so we ban selling data and then people who want it will buy or even fund breaches instead. Massive breaches will likely become more common, because that's how driving valuable stuff into a black market always works, and companies who aggregate data already do a shit job protecting said data and face negligible consequences from regulators or markets for this. Even the press will happily blame the constant stream of leaked data on unnamed "hackers" every single time

I also expect to see a shift to buying more "data-driven insights" from big data aggregators, which in practice will mean the same thing as buying the data means now, just with the middlemen rearranged slightly

Governments will still be able to subpeona the data in ways that route around human rights and on the rare occasions where this comes to light, "national security" and the need to fight whatever war - whether against a concrete nation or organization or an abstract concept - they believe will most muddy the waters to cite