Why were the Prohibitionists concerned about the consumption of alcohol?

Prohibitionists in groups such as the Women's Christian Temperance Union were concerned about the negative effects of alcohol consumption and alcoholism on families. Families could be left destitute when a family member, often the male breadwinner, drank away his earnings at the bar or even ran off, deserting the family.
Prohibitionists also understood the relationship between excessive drinking and domestic violence. They hoped that banning alcohol would lead to fewer injuries from domestic assault.
In addition to promoting legislation to ban or prohibit alcohol sales, prohibitionists tried to come up with alternatives to alcohol, such as root beer, and to establish social venues, such as ice cream parlors and soda fountains, as alternatives to bars serving liquor. In fact, many soda fountain owners and tea companies supported prohibition as a way to increase sales of their products.
Prohibitionists such as those in the Anti-Saloon League also feared that political campaigners were entering immigrant bars and promising jobs and favors in return for votes. They wanted to end this corrupt practice.
In January 1919, the Eighteenth Amendment was ratified, leading to fourteen years of legal prohibition of alcohol.