Trouble is, drunkenness is on top of all those other factors, not an alternative. And drunkenness has an effect of causing people to unrealistically underestimate the risks associated with many of the other factors, an dthus be less cautious than they otherwise would be. IOW, yes a 75 year old driver is statistically equivalent to the mildly intoxicated middle aged driver. But the 75 year old whose had a drink or two, is not only more impaired than before, but also less able to perceive the degree of risk associated with either form of impairment. An unintoxicated 75 year old is usually well aware that his/reflexes aren't what they used to be, and that he/she needs to be extra careful while driving. A mildly intoxicated 75 year old will often be oblivious to those facts.
"Obviously, I'm against drunk driving, but it depends what you define drunk driving as..."
That rhetoricly asked, unanswerable (without endless deabte) question is exactly WHERE BAC came from.
BAC establishes a limit that is standard for every person. EQUALLY. The law (at least here) is based on the equality under the law while it also removes the endless debate.
"drunk" isn't the issue under the law at all, BAC is what the law reflects. A level is established by elected representatives, the way it should be in a represntative republic. SO then it seems you oppose a representative republic's way of forming the law. How conservative of you.