Government may not forbid the expression of an idea simply because society finds the idea itself offensive or disagreeable. The right to free expression is meaningless if that right only protects expression sanctioned by the majority. Strong nations tolerate dissenting expression.
Weak nations suppress it.
It is that simple. But one of the things that makes this country the greatest and freest in the world, is that we protect free expression even when we hate the message and despise the messenger. In 200 years, the Bill of Rights has never, never, been curtailed. This country has gone through a Civil War, two World Wars, and a Great Depression - monumental events which tested our strength and unity. But in those moments, we resisted the temptation to cut back individual freedom.