Hi Bart.  
I assume your question was honest.  And offer an honest answer
Extensive writings left by America’s Founders fully explain why they designed America’s new form of government as they did - including the 2nd amendment. But HI’s schools no longer teach them. So all I can offer is this simplified summary
Powerful men never have to fight: No one’s foolish enough to pick on them. Switzerland didn’t require citizens to own automatic weapons to defeat an invader: Just to make the cost of invading too high to be worth it
An example? Ok. Lexington’s “Shot Heard Round the World”
Hitler’s rise to power required Germany’s People let government disarm them. They did. Later none could resist his still-armed Nazis. Brutal tyranny followed
A corrupt old Monarchy sent soldiers to disarm New World colonists. They refused. America was born. And w/o America today we’d all be living under WW-II’s brutal Nazi-Fascist-Shinto Alliance that had already defeated all the world – except for America