The reason why the Second Amendment allows so many guns in America is, according to the Founding Fathers, a last resort if tyranny were to overtake us as it did in the 1700's. They realized that no man was perfect and that it was likely that at some point in the future, blood would need to be shed to maintain liberty.
"The tree of liberty must be refreshed from time to time with the blood of patriots and tyrants."
- Thomas Jefferson
"Every citizen should be a soldier. This was the case with the Greeks and Romans, and must be that of every free state."
- Thomas Jefferson
"The beauty of the second amendment is that it will not be needed until they try to take it."
-Thomas Jefferson
"They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety."
-Benjamin Franklin, Historical Review of Pennsylvania, 1759.
"To disarm the people (is) the best and most effectual way to enslave them."
-- George Mason
"... who are the militia, if they be not the people of this country...? I ask, who are the militia? They consist of now of the whole people, except a few public officers."
-- George Mason
The list goes on. The point is that these men faced oppression far greater than just about any of us ever have, and after having their freedoms and liberties stripped one by one decided to ensure, to the best of their ability, that it would never happen again to anyone in America. While you may not agree with the Founding Fathers on all points, they were there in a period of true rebellion and war in what is now, thanks to them, the United States of America.
Some things never change, and one of them is the corruption of power.
tl;dr: There is a historical precedent for it and, being right after the amendment guaranteeing freedom of speech and all that, it was clearly important to those who formed this country. Some things don't change as much as we'd like them to, and one of them is human nature.