There is nothing in the Bible that would prohibit one from drinking alcoholic beverages in moderation.  There is a prohibition against drunkenness, however.¹  This being true, "Why do we (myself included) teach that the drinking of alcohol is wrong?"

Keep in mind that it would be very hard to find anyone who could say that no one in their family has ever been touched by the devastating effects of alcohol; such as alcoholism, liver damage, death and injury of self and others.  This being true, then God's children should set the example as the light of the world and the salt of the earth.²

Although it might be permissible to drink alcoholic beverages in moderation, the question is "Is it beneficial to do so?"  As the apostle Paul wrote, "Everything is permissible but not everything is beneficial.  'Everything is permissible but not everything is constructive.  Nobody should seek his own good, but the good of others."³

It's possible that your drinking of alcoholic beverages might encourage someone who has a drinking problem to also drink; your example might cause them to stumble.  The apostle Paul wrote that it is better not to drink wine or to do anything else that will cause your brother to fall.⁴

Bible References:

¹ (Galatians 5:21)

² (Matthew 5:13-16)

³ (1 Corinthians 10:23-24   NIV)

⁴ (Romans 14:21)