Why are firearms sold to the public in the States?

I am from England. Here, even police officers are not allowed to carry guns on them. Public ownership/licensing of firearms is not even thought to be normal. Due to the recent mass shootings in the USA, I’ve come to realise just how easy it is to buy a firearm over there. So I’m trying to understand it from an American citizen’s point of view…
Do you think it’s okay for an everyday citizen to own a gun?
Why do you think public ownership of firearms is needed?
Would you do anything to maybe change or tweak the laws a little bit?