Historically the US federal government has never collected more than 20% of GDP in taxes. Doesn't really matter what the tax rates are. The US needs to get out of debt and I think ending wars is the way to do that.
Someone have to pick up the bill and I have a hard time seeing who that could be besides the american taxpayers.
And just because it hasn't been done before is obvious no natural law
The money that you save by not having a military, can go to buying other goods that those ex-soldiers can provide.
I think Cuban was right that we do have a spending problem. We spend too much on things that are not important. We should cut debt, but the debate around this issue has been framed as a false and confusing dichotomy by the two major political parties.