You're right. The government can not control behavior.
The purpose of laws should be to provide punishment and restitution for damages to others. There is an inherent negative consequence for irresponsible behavior without trying to draw arbitrary lines.
Example: Keeping a gun in my home should be legal. Shooting my gun should be legal. If I shoot someone else's car, I pay for the damages. If I shoot a person, I pay their medical expenses and go to jail. We can criminalize things without drawing arbitrary lines around 'irresponsible' behaviors.
I know there's a certain mantra on this site that the only laws we should have are those that address actions that have uniquely identifiable victims. While I agree with this to a large extent, how does one address things as simple as littering public roadways? Or vandalism to public parks? Some laws are necessary to protect the public interest--where you cannot affix a singular name to a complaint or even identify all the victims of an action.
But I agree that some folks can safely drive with a BAC > 0.08; some can drive and text; and 50 MPH speed limits may not be necessary on roadways at times when traffic is very light...some of us can actually drive without wearing our seat belts.