It's the only drug I've ever had a problem with, so I'm biased, but I'd say alcohol is certainly one of the worst.
- You can die of the withdrawals
- It's extremely bad for your health; you will die if you keep it up for a long time
- You can't function on it as well as you can with opiates. After a while of being an alcoholic, you either can't function because you're in withdrawals, or because you're drunk. It becomes harder to tread the line between the two and keep well enough yet sobre enough to hold down a job (I've never got to that stage though, this is based on what I've been told)
- When you quit you are reminded of it constantly due to its social acceptability, and the fact that it pervades every avenue of Western society
I'm not saying it's worse than heroin or meth or crack or benzos because there's other disadvantages to those. But it's not to be taken lightly.