WTF? What did Truman do that made the whole world worse off?
The dropping of the atomic bomb on civilians in Japan was inhuman, especially considering that the Japanese had sued for peace earlier on in 1944 an 1945. The Korean War gave birth to the undeclared war- "The Police Action." Truman's overzealous responses to the Soviet Union led to the unnecessary Cold War and the birth of the CIA police state. George F. Kennan, his National Security Adviser, gave birth to the idea of perpetual wars of "containment" that led to Vietnam, Nicaragua and Haiti throughout the Col War.
Truman's modern military budgets during the the illegal Korean War helped give birth to the military-industrial complex. His recognition of the state of Israel has tied American interests to the Middle East and the countless, complex issues which affect that powder keg. Thus, Harry Truman's administration gave birth to the idea of undeclared "wars" and the American Middle Eastern policy that had killed so many and all sides. That hurt the world.
Furthermore, Truman's outrageous corruption in his administration certainly hurt society. The IRS frauds and "mink coat bribery" were straight out of Boss Pendergast's Kansas City, however, they were being done in the White House, not a flop house. Truman was disgustingly corrupt. Also, his deranged economic theories in the form of the "Fair Deal" paved the way for the wasteful "Great Society" of Lyndon Johnson (who is the second worst president in the United States).
You and others may like the things I have listed and that's cool. I'm a classical liberal and thus I do not. Thus, for dropping atomic bombs that killed thousands of Japanese non-combatants; for creating the CIA with a mandate to destroy undesirable democracy around the world via assassination and coups; for instigating the Cold War with the help of George F. Kennan; for his illegal, unjust involvement in the Korean War; and for playing a major role in the establishment of American policy in the Middle East and Israel; for his massive corruption and for paving the way for the modern welfare state Harry Truman should be known as the worst president in US history.