Sometimes it is the only way to get your car back to your home. If you leave the car in the bar parking lot, it will be towed. So you can either drive it, or pay a massive impound fee. It might sound bad, but honestly who else is on the street at 2am? You are only a risk too yourself, and other drunk drivers. Yes, if you get pulled over you risk a DUI, but a chance of a DUI is better than definite impound fee.
Yeah, every so often a family might get hit, but really all that means is fewer children screaming in restaurants, and really that is something we can all enjoy. Also, who are these people driving around at night with there children? I submit to you they are overwhelmed parents looking for a way out. Drunk drivers are just the tool they chose to use, like a much lazier version of "suicide by cop".
Also, there is something worse than drunk driving, it is driving while an asshole.