I think 80mg is fine in theory, but I know that alcohol can affect people in different ways and even the same people on different days, I speak from experience. Now here is where I have to tread carefully with what I'm saying...
I know a few people who are affected the same or worse by 1 or 2 pints, as what I am by 5 or 6 pints on a good day. My tolerance is generally fairly good, but there are some days where I consume 3 pints and feel as if I've had double that. Of course there are lots of factors behind that: how I've eaten, how much sleep I've had, stress - all can affect (from personal experience) how much I can/can't drink. I have no doubt that on some occasions after 4-6 pints of beer (albeit over 4-5 hours) I could drive (at least ride a motorcycle), whereas other people couldn't drink more than 2-3 in that same time period and do so.
Drink driving should be punished by severity but as I've said above, people have different tolerances towards alcohol. There are some people for who 2 beers, is say just as dangerous as someone else after 5. I've ridden a motorcycle after 2 beers and actually felt less affected than what I have when I've ridden totally sober but very tired, at 2 beers I've felt fine. Tiredness is very dangerous and its a hidden danger, only the person affected by it, can safely judge it. You cannot measure tiredness with a technological aid, and you have to rely on people to make their own judgements. Tiredness affects judgement, reaction times almost as much as what alcohol can and I've realised that, in the morning on my ride to work I'm far more likely to be awake and alert than by late afternoon when I'm going home.
Alcohol affects everyone differently, just as tiredness does and unfortunately whilst a one size fits all solution is not ideal, its the only practical option. Cutting it down to 50mg may not make much difference to accident rates, but it would certainly deter those 'with lower tolerance' to even the smallest amount of alcohol from driving.