it's not the tannins in wine that are good for you, it's the color chemicals, i forget what they are called... maybe anthocyanins or some name like this. reservatrol is one specifically in red (ie purple) grape skins. there is also some amounts of others as well.
but yeah, the marketing machine for alcohol is intense. it's fine to drink a pint of beer or cider daily but beyond that it rapidly turns into poison. in fact it probably is actually beneficial to have a small amount.
i figure that is probably due to evolution and humans being meat/root/leaf/fruit eaters, all ripe and near over-ripe fruit have a little in them, and all those color chemicals protect against the damage caused by sugars.