Tired drivers can be as dangerous as drunk drivers. Probably tired people can cause as much domestic strife as drunk people. Depression is another disabling factor. The last two we don't legislate for.
A few years ago, there was a major rail crash in the UK caused by poor maintenance. To save money, the contractor had cut down on inspection, and a broken rail brought a 100mph train to ground, killing many. The accountant who took the decision to reduce standards was stone cold sober. At the same time, a rail employee who sold you a ticket while drunk, or even not drunk but having taken alcohol at work, would have been open to instant dismissal, and could even have been jailed.
A friend has deteriorated to the point where, though formerly an excellent fiddler, he can no longer play reliably or often even tolerably. He resents anyone criticising his playing even in the mildest way, and is likely to threaten them with violence. He has been barred from almost every session for many miles around. He was abused as a child.
Another friend's father was dying painfully of cancer. Being a strict Dutch Calvinist, he abhorred the use of alcohol in excess, but it was the only thing he would take that would keep the pain within limits. His daughter would supply him with a small bottle of Jenever at the start of the day, and when he fell asleep, quietly top it up so it was always about two thirds full. He was drinking two or even three full bottles a day, but because he didn't know it, both he retained his self respect and a degree of comfort.