Should betting on sports, or any other form of gambling, be legal?
The first question is: Who decides?
Until a few decades ago, no one would have thought the decision-maker was the federal government. In fact, for the first 150 years of American history, Congress had almost no role in matters that affected people's daily lives. It was entirely up to the states to decide not only whether gambling should be a crime, but whether anything should be a crime.
Since the birth of television, it has become difficult to appreciate that the federal government is a government of limited power. If it is not in the U.S. Constitution, Congress, federal courts, administrative agencies and even the President simply do not have the right to tell people what they can and cannot do in their private lives. It was, and remains, except to the extent they have voluntarily given up some of their power, state governments that have unlimited power.