Free trade gives individuals the freedom to decide what goods and services are best for them by providing more products from which to choose. Tariffs and other forms of protectionism reduce freedom because a politically motivated government influences or decides what is available and/or affordable. This is inherently wrong because the government should not be in the business of reducing freedom for its citizens; particular when doing so increases their costs of living and lowers their quality of life.
Free trade also advances peace. Countries that actively trade with each other are much less likely to go to war. Doing so would be make no economic sense because if you destroy your enemy, you can’t trade with them anymore. Citizens and companies have a vested interest in peace because war, or even the threat of it, would negatively affect their lives. Before World War II, Germany and France as well as France and Great Britain engaged in frequent wars. After WWII, the idea of free trade in Europe emerged and eventually developed into the European Union. For more than 65 years there have been no wars between Europe Union nations, or even the threat of any. The strong economic ties between the US and Canada provide a similar peace benefit.
I have long believed in free trade and minimal government involvement in economic affairs; and most other affairs as well. The less government is involved in the economy the better; particularly attempts to redistribute wealth and do things for people that they can do themselves. Politicians are incapable of making sound financial decisions; just look at all governments with massive debt and the resulting economic problems they cause. They confound most everything they attempt to fix (education, health care, retirement, taxes, etc.). Government should be limited to national defense and protecting people from the types of harm from which they cannot protect themselves (pollution, crime, etc.).
Check out this video series by Milton Friedman to learn more about these issues: http://www.freetochoose.tv