You are right - the government does have the right to determine how much you can drink and then drive. But your reasons are wrong.
The government has the right to set limits on alcohol and driving because driving on public roads is a privelege, not a right. You must earn the privelege to drive. And to retain the privelege you must abide by certain rules.
However, if I own a couple thousand acres and choose to get rip roaring drunk and drive on that land - the government has no say in the matter. It's my private property. If in doing so I injure someone - there are laws involving assault to deal with that. There are also laws dealing with trespass. If I didn't invite you on my land and you get hurt you have no one to blame but yourself for being somewhere you shouldn't be.
By entering a restaurant you are entering into a contract with the proprietor of your own free will.