The argument is “Do you believe people with AR-15s” can defend against the US military? The answer is yes, no, and it depends. Let’s look at some numbers and assumptions (not perfect I know )
There are about 3M active personal across all branches of the military.
Not all 3M are combat roles. Tooth to tail ratios will come into play.
There are probably around 160M people fighting age (Ages 18 – 65).
There about 12M veterans
The continental US is much larger than Iraq and Afghanistan. This makes logistical support much harder
Defending is a lot harder than attacking.
The unknown of outside powers
Based on the above I believe that the citizens would win. 3M is not a lot of troops to hold a country as large as the US. And holding cities and key infrastructure takes a massive amount of troops, will, and logistical support. Iraq and Afghanistan have clearly shown that a technological inferior enemy can still “win” (think of overall money/lives lost/state of the countries now/etc) and the populations and size of the countries are much smaller.
Then you have tooth to tail rations to think about. If you don’t know what this is it means for a Combat Role (X) there needs to be (Y) amount of support staff for that combat role to be used/be effective. The current ratio for infantry is 1:7. Meaning you need 7 support people for that 1 infantry person to be effective. For fighter plans the ratios are much higher (I have seen figures 1:50. Maintenance, arms, flight planning, etc,).
So let’s say a f-15 pilot (or drone pilot) is ordered to bomb fellow citizens. If the pilot says yes and the support says yes the mission can happen. If the pilot says no and the support says yes the mission can’t happen (who is going to fly the plane the guy who refuels the aircraft?). If the pilot yes and the support says no the mission can’t happen (i.e. that one pilot is not getting the plane all ready to go). If the pilot says yes and not all 50 say yes then the mission can happen but at reduced efficiency.
Also if the military is used on the civilians the question becomes what percentage of the military will obey the order? 100% would not support the order, nor would 100% jump to the other side. So somewhere in between which means the military would be operating at a reduced efficiency. Plus defending something is a lot harder than attacking it. The defenders have to be alert 100% of the time while those attacking only have to be alert when they attack. If the US military is trying to defend a lot of critical infrastructure at once (electric, water, cities, food, ammunition, fuel, etc). The amount of combat troops they will have to launch attacks will be greatly reduced.
Sure you could maybe do conscription but history/data has shown that conscripted troops are less effective and could cause larger parts of the population to turn against you.
Also high tech weaponry (like drones, tanks, HIMARs, etc.) require huge logistical support. Disrupting that support (given size of country, number of civilians, etc) would probably not be as difficult as people think it is. Then you have to think about ROE. A lot would also depend of the ROE used and how evil the government is. Don’t care about your cities/population then artillery/bombing runs/etc. can start to mess up cities at the cost of the people hating you more. Decide the ROE is to spare cities and people then your artillery/bombers/etc are pretty useless.
I think the key comes down to which sides the citizens decide to support. The veterans will be able to provide military experience and tactics for those who oppose the military. The military itself will fracture. And who knows what the outside powers will do? Of course they will get involved but in what fashion (selling arms, sending over troops, taking land, etc).