That's debatable. It's kind of like banning meth: people want it anyway, so they blow up suburban houses trying to make it. If they could just buy it at CVS, there would be more methheads but fewer meth labs. It's all about how you want to tune the numbers, and the same applies to tweeting while driving. (Twitter on the speedometer: less distraction, more temptation. Twitter not on the speedometer: less temptation, more distraction. Both are bad.)

I'm not sure this analogy applies. You're talking about a drug with addictive versus a social network that, for most reasonable people, I would imagine, is not necessary to access when you're driving. In fact I'd be willing to bet that most people would agree this is a bad idea, until you actually put it in front of them.