Mikey already made one of the points: "The only potential negative is that the government will coerce these companies into providing their data, which if it isn't anonymized, could be used against you in court or other legal proceeding."
As if that was the ONLY potential negative here... Are you cool if one of these private companies leaks your activity and now your mom/boss/kids know every time you've ever masturbated to anime porn?
The shit's going in the wrong direction, IMO, that's all. "Nobody cares about you, you're a nobody" is great unless you actually have people who care about you...