Why do religions ban alcohol?

I read in my Bible that drunkenness is banned, but that a little strong drink is good for the stomach. Jesus turned the water into wine at a wedding. I've heard it said that it was just juice, but yet it goes on to say it was the best wine of the night. The Greek word there translates to "wine", not juice. Other places, such as in Mark where they talk about putting new wine into old wineskins, could be interpreted as juice as it hasn't fermented yet. But that specifies new wine and the word, "wine" is still the same Greek word.