The
point that you're missing,
Saige, is that
nuclear weapons in this context are as a
deterrent, rather than an actual offensive tool.
The USA, being the (arguably) most important, powerful country in the world needs to have something to defend itself with. Because there are plenty of crazy people out there who, with enough determination, could get a hold of nuclear weaponry, and thusly endanger the good of the American people. By retaining an arsenal of nuclear weapons, it ensures that nobody will attack them, for fear of retaliation.
It's a hard fact to accept that nuclear weapons are now the end of the line in terms of self-defense, but as of 1945, the bar had been raised. In a perfect world, we could un-invent the bomb and not have to worry about it anymore. But now that nuclear weapons are in existence, a country the size and power of the USA not owning some would be ridiculous.