While it hasn't come up recently in any of my own arguments, the whole "why don't we have privately funded defenses?" question seems to be ably put down here. So all of you who were sharpening that particular argumentative knife are pleased to be putting it back now.
We do have a privately funded defense. It's called "Second Amendment Rights."
Interestingly, we also have public health care. It's called "Medicaid."
The problem liberals have with both these things is that they can't bear letting people make their own decisions, because some people might make bad decisions. Instead, they have to eliminate individual choice in as many things as possible, by eliminating both privately owned firearms and privately funded heath care. Then they can force everyone to choose the worst option.