Because the country would not be "free" without the right to express your opinions
In this way the Declaration of Independence makes is crystal clear that government has one overarching purpose; that of protecting the inherent human rights of life, liberty and property (pursuit of happiness).
There were lots of foreign changes that presented challenges for the US. I'll give you a few examples from different time periods. First would be when England wanted to tax the Americans in the Revolutionary period. They did this to try and restrict America's freedom. Another example would be that Russia had spies during the cold war period. This was to gain intelligence of the US war plans. Also when Germany sent the Zimmerman Telegram to Mexico during the WWII period. This was to get Mexico to launch a surprise attack on the US.
