Let me preface by saying it's terrible when this happens to anyone and the people who do it are pieces of shit.

That being said, maybe just don't drink poison in public spaces? I've never understood how anyone can possibly enjoy going to a place where it's too loud to have a conversation, everyone is incapacitated and annoying and then you slightly poison yourself so you can feel better about acting the same way. If getting drugged is that big of a concern, maybe the answer is stop being an alcoholic and go to a support group instead.

To help understand my point of view, imagine if this were an obese person concerned about having their cake contaminated/drugged and instead of just putting down the fork they get a plexiglass cake dome. It's already bad for you, maybe it'd be much simpler, healthier and safer to stop eating cake.