I think abuse potential is key here. Having the governments enforce strictly requires a lot of observations and tools that can readily be abused for all kinds of shit.
Something being difficult to legislate doesn't absolve the need for legislation. Police are arguably much more destructive and prone to abuse and corruption, but the solution is not to legalize theft.
The whole point of legislation is to draw lines along slippery slopes, I would think that the potential for abuse exists in almost every law ever written.
