The Founders lived in an environment where the Atlantic Ocean was a pretty good protection from foreign invasions, and several month's time would be available to prepare a defense once hostilities broke out. For Indian attacks, the state militias were not only sufficient but also more effective in most cases.
While we had a small standing federal Army for much of our early history, we did have a standing federal Army, and later on a permanent federal Navy, for most of our history. The United States Military Academy at West Point was established for a reason.
If you want to debate the appropriate size of a standing federal Army and Navy, or the relative size of the active duty and reserve components, or the appropriate relationship between the federal active duty forces and the state controlled National Guard, fine. Those are legitimate questions, though I believe World War II showed beyond the slightest question that America's long history of being woefully unprepared for major wars did not serve us well and was unrealistic in the age of intercontinental ballistic missiles and the huge standing armies of the former Soviet Union.
But if you want to argue that standing armies are unconstitutional, you can't get that even from the earliest days of the American Republic. We learned our lesson in the ramp-up to the War of 1812.
I, for one, am not interested in seeing a foreign Army attack Washington DC, burn the Capitol, the White House, and virtually every government building except the home of the Marine Corps Commandant, as actually happened during that war. There are consequences to failure to prepare militarily for an enemy attack. Those consequences will be far worse today than they were in the early 1800s.
I do not mind a Navy to patrol the waters, that has always been accepted. What the Founders warned against was a professional and standing army which we have now.
I do not support it and I do not support their missions which are often ill defined and in the case of Iraq based on lies. We have already been in Afghanistan and Iraq for 10+ years, these are the longest ‘wars’ in US history.
As for the people in the military themselves, they’re there for a paycheck and yes, they’re brave and good people but they should object and not kill other humans in these ill defined adventures overseas. Sorry, I find it hard to buy into the propaganda.