I'd argue that the purpose is to act as a deterrent against countries that might otherwise think of invading their neighbors or things along those lines, but it's reasonable to think that the cost of such of large military is not worth the benefits.

It's also one of the US's largest employers.

And one of our largest welfare programs. It's pretty easy for an 18 year old with no marketable skills to join the military and end up with some skills and a free college education.

> ... which is often used to conduct evil, ...

I am curious. In your eyes, what evil has the US military done?