Corrections in red.  Stylistics in blue.

The USA Today  

Today I saw on television that in United States there has been another shooting/gun incident at a school.
I think that they are different from the rest of word, because they want to allow the free possession of weapons.  I think that if they forbade/prohibited this, perhaps they wouldn't have so much gunfire.
As there are many Americans, I want ask their opinions.

I believe that every person has the natural right of self defense, and also the concomitant right of possessing tools that make self-defense possible.  The best tool for that purpose is a firearm.  

In every place where guns are outlawed, such laws are obeyed only by good, law-abiding people.  Criminals pay no attention to such laws.  So society is left in a state where criminals have such weapons, and individuals and families have none with which to protect themselves.  That is immoral.

Citizen possession of firearms is also an important tool to prevent the installation of a tyrannical government. It is typical of dictators and would-be dictators to tightly control the private ownership of firearms.