Why is "blacking out" a warning sign of alcoholism?

Answer 1

People without a tolerance to alcohol will usually get very sick and pass out (become unconscious)when drinking too much. Blacking out, in which the individual continues to walk, talk, etc. (although he or she may do things that are out of character) but has no memory of it the next day indicates that the tolerance level has increased, as has the toxicity level (level at which the individual has alcohol poisoning). Increased tolerance and toxicity levels are signs of alcoholism since it takes a lot of drinking (in the vast majority of cases) for these to occur.
Other signs of alcoholism include withdrawal symptoms (tremors, seizures, DT's and even death) as well as repeated use in the face of negative consequences. Often the alcoholic will place priority in drinking while family, work, etc. become less important.

Answer 2

If you drink so much that you literally black out, that indicates a problem. Most people can drink and remember what they did the next day. If someone drinks so much that they can't, that's not a good sign for them. That's what an alcoholic does....they drink so much that they black out.