Well, there is drunk and drunk.
From about 15 to 22 years old i've been an heroin addict, i dropped school and spent my life selling and taking drugs in free partys, heroin/cc/ketamine/lsd mainly, but also weed and so on. I played eve online at the time to escape, i had in-game responsibilities and often helped organize the fights while on drugs, it might have been an issue maybe 4/5 times in years.
Of course people shouldn't play ranked while being totally drunk. But trust me you'll have an hard time proving that they were :)
I'm sure there is countless people playing while smoking weed or other craps, but statistically the enemy team will have high people in their team as much as you have sometime one drunk dude in yours.
What about people playing while not having slept for more than 72hours, should they be punished too, what about those that can't concentrate because they have a headache, those that have issues with focusing their attention, should they be punished too ?
Most of us play league to relax and escape our problems for a bit. for some of us relaxing and such also mean having a little drink.
I agree that if you are way too drunk you should not play, but riot won't have a way to prove you were unless you say it, what about if you contest the punishment saying you were joking ?
I still take opiates as a treatment today, what about that ? should i not be allowed to play because of the side effects ?
I don't think it's feasible and today I still wanna be able to play league after a few beers.