The main reason you can't legally make liquor at home in the U.S. is because of taxes. Typically, for each 750-milliliter bottle of 80-proof liquor, the federal government charges an excise tax of $2.14. In addition, state governments charge an excise tax (in Alaska, it's nearly $13 a gallon). This means that for each gallon (4 liters) of moonshine, the government is losing out on up to $25. (The beer tax is only 5 cents per can, and the wine tax is 21 cents per bottle for wine with alcohol content under 14 percent) [source: Snider].
The lost revenue can add up. In 2000, Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) agents uncovered one store in Virginia selling enough raw moonshine materials to produce 1.4 million gallons (5.2 million liters) of liquor worth nearly $20 million in lost tax revenue [source: Tsai].
To make moonshine (also known as white whiskey, hooch, rotgut, corn liquor or white lightnin') legally, you need federal permits and licenses. To obtain these, you need to cover the startup costs of operating a distillery that meets the federal government's standards, and this can range into the millions, even before you get your license [source: Yeldell].
Then you'll need to contend with those who say that legal moonshine, by definition, can't really be moonshine at all.