Cases where there are abusive, disruptive parents should definitely have their child or children taken away from them, as the children would live in improved conditions if they are placed in better conditions, that is. Looking at it on a average scale, alcoholics do tend to be negative for the child or for the children, leading to future problems.
Yes, they should be. An ounce of prevention is better than an ounce of cure. Assuming of course that when these children of alcoholics are taken away, they are given better living conditions than they initially had with their drunken parents, and their education and moral development are considered top priorities, then I agree. You cannot just take children away from a bad influence, only to put them in another bad place with equally hollow values. The care system that will hold these children must be up to the job.
My best friend's dad is a heavy alcoholic and is actually still a GREAT dad. His addiction to alcohol is clearly a problem, but it doesn't outweigh the fact that he does everything possible to help out his son. He's attempted to stop drinking several times but ends up in the hospital after having seizures from withdrawal. All he lives on is his disability checks and yet he's still putting money aside to get my friend a new car. Being an alcoholic doesn't completely corrupt a parent in every case.