The actual problem is one of power and intention. Yes, version control would make earmarks obvious. Yes, it would make tracking contributors (lobbies) easier. Yes, it would make tailoring tried and trusted legal documents easy.
All of these are reasons why version control will never be applied to the law. We want these things, but we are not the customer. The real customer is actively trying to prevent these things from ever happening.
The reality is that these tools are probably already being used for these exact purposes - in private, and for personal gain.
I even registered gitlaw.us a few years ago and then let it expire because I couldn't bridge the impedance mismatch between the idea and the implementation.
But again, I would never voice such thoughts, for many reasons:
1. It's exactly the attitude that your 'real customers' want in the public - learned helplessness.
2. You start believing it, and there is an insidious, negative effect on your judgement, decisions, and life. I'm not saying be a rose-tinted-glasses optimist, but don't be the opposite extreme either.
3. It is possible to win. Remember Gandi, Mandela, etc. Imagine how bleak their outlook was, yet they remained committed, steadfast, relentless, constant as the dawn, and eventually the time came for their ideas and there was nothing more powerful or unstoppable.
4. Real hackers aren't like that. The bigger the problem, the bigger the opportunity for disruption and making the world better. There are few bigger than this.
It takes efforts like these to eventually make the time come for the ideas that change the world, so it behooves us all never to talk them down out of mere pessimism. Constructively criticize yes, but no shootdowns.
Remember, first they ignore you, then they ridicule you, then they fight you, then you win.
It can be done.